Rearrange and simplify text a bit, also put examples early

Most users want to see the examples as early as possible, so we place
them directly after the new (simplified) introduction.  The examples
have been rewritten to separate commands from options and grouping
the command with its value, where applicable.

The rest of the document has just been auto-filled to fit to < 72
columns and sections now use === and ---- for headings to make the
README more accessible from a terminal.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

README.md

@@ -1,74 +1,97 @@
-# Light
+Light - A Program to Control Backlight Controllers
+==================================================
 
-Copyright (C) 2012 - 2014, Fredrik Haikarainen
-This is free software, see the source for copying conditions.  There is NO
-warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE
+- [Introduction](#introduction)
+- [Examples](#examples)
+- [Usage](#usage)
+  - [Operation modes](#operation-modes)
+  - [Value modes](#value-modes)
+  - [Target](#target)
+  - [Field](#field)
+  - [Controller modes](#controller-modes)
+- [Installation](#installation)
+  - [Arch Linux](#arch-linux)
+  - [Manual](#manual)
+  - [Permissions](#permissions)
+- [Origin & References](#origin--references)
 
 
-## Description
+Introduction
+------------
 
-Light is a program to control backlight controllers under GNU/Linux, it is the successor of lightscript, which was a bash script with the same purpose, and tries to maintain the same functionality.
+[Light][] is a program to control backlight controllers under GNU/Linux:
 
+* Works, in particular when other software, e.g. xbacklight, does not
+* Does not rely on X
+* Automatically detects the best controller
+* Possibility to set a minimum brightness value
 
-## Features
+Let's get started with a few examples, for details, see below for the
+full description of the different operating modes, value conversion and
+how to operate different controllers.
 
-* Works excellent where other software have been proven unusable or problematic, thanks to how it operates internally and the fact that it does not rely on X.
-* Can automatically figure out the best controller to use, making full use of underlying hardware.
-* Possibility to set a minimum brightness value, as some controllers set the screen to be pitch black at a vaĺue of 0 (or higher).
 
+Examples
+--------
 
-## Installation
+Get the current brightness in percent
 
-### Arch Linux
+    light -G
 
-If you run Arch Linux, there exists 2 packages;
-* [light-git](https://aur.archlinux.org/packages/light-git) - For the absolutely latest version
-* [light](https://aur.archlinux.org/packages/light) - For the latest tagged release
+or
 
-I recommend you go with light-git as you might miss important features and bugfixes if you do not.
+     light
 
-### Manual
+Increase brightness by 5 percent
 
-We recommended downloading a versioned tarball from the relases page on
-GitHub.  Download and untar the archive:
+    light -A 5
 
-    tar xf light-x.yy.tar.gz
-    cd light-x.yy/
-    ./configure && make
-    sudo make install
+Set the minimum cap to 2 in raw value on the acpi_video0 controller:
 
-However, should you want to try the latest GitHub source you first need
-to clone the repository and run the `autogen.sh` script.  This requires
-`automake` and `autoconf` to be installed on your system.
+    light -cr -s acpi_video0 -S 2
 
-    ./autogen.sh
-    ./configure && make
-    sudo make install
+Try to set the brightness to 0 after that, it will be changed to the
+minimum 2:
 
-The `configure` script and `Makefile.in` files are not part of GIT
-because they are generated at release time with `make release`.
+    light -r -s acpi_video0 -S 0
 
+Find keyboard controllers:
 
-### Permissions
+    light -k -L
+
+Activate `ScrollLock` LED, here `input15` is used, but this varies
+between different systems:
 
-**Optional:** If you want to use udev rules instead of suid to manage sysfs permissions, you may skip the `make install` step and instead add something like the following to `/etc/udev/rules.d/90-backlight.rules` after copying your binaries:
-```
-ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chgrp video /sys/class/backlight/%k/brightness"
-ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chmod g+w /sys/class/backlight/%k/brightness"
-```
+    light -k -s "input15::scrolllock" -S 100
 
+Usually, LEDs only take 0 or 1 in raw value (i.e. for off/on), so you
+can instead write:
 
-## Usage
+    light -kr -s "input15::scrolllock" -S 1
 
-This application usually has 5 different criteria on flags to use, which are operation modes, value mode, target, field and controller mode. Flags from these different modes can never be used in conjunction, but all of them do not always have to be specified (although it is recommended to do so for verbosity).
+Verify by reading back the max brightness, you should get a value of 1:
 
-**Note:** This application will only print errors if you are using it incorrectly. If something goes wrong, and you can't figure out why, try setting the verbosity flag with -v:
+    light -kr -m -s "input15::scrolllock
+
+
+Usage
+-----
+
+Light has 5 different criteria on flags to use: operation modes, value
+mode, target, field and controller mode.  Flags from these different
+modes can never be used in conjunction, i.e. you cannot get and set a
+value at the same time, that requires different invocations.
+
+**Note:** like most UNIX applications, light only print errors if you
+  are using it incorrectly. If something goes wrong, and you can't
+  figure out why, try setting the verbosity flag with -v:
 
 * 0: No debug output
 * 1: Errors
 * 2: Errors, warnings
 * 3: Errors, warnings, notices
 
+
 ### Operation modes
 
 The operation modes describe **what** you want to do.
@@ -81,16 +104,26 @@ The operation modes describe **what** you want to do.
 * -I: Restore the previously saved brightness (usually used on boot)
 * -L: List the available controllers
 
-When used by themselves operate on the brightness of a controller that is selected automatically. S, A and U needs another argument -- except for the main 4 criteria -- which is the value to set/add/subtract.   This can be specified either in percent or in raw values, but remember to specify the value mode (read below) if you want to write raw values.
+When used by themselves operate on the brightness of a controller that
+is selected automatically. S, A and U needs another argument -- except
+for the main 4 criteria -- which is the value to set/add/subtract.  This
+can be specified either in percent or in raw values, but remember to
+specify the value mode (read below) if you want to write raw values.
+
 
 ### Value modes
 
-The value mode specify in what unit you want to read or write values in. The default one (if not specified) is in percent, the other one is raw mode and should always be used when you need very precise values (or only have a controller with a very small amount of brightness levels).
+The value mode specify in what unit you want to read or write values
+in. The default one (if not specified) is in percent, the other one is
+raw mode and should always be used when you need very precise values (or
+only have a controller with a very small amount of brightness levels).
 
 * -p: Percent
 * -r: Raw mode
 
-Remember, this is the unit that will be used when you set, get, add or subtract brightness values.
+Remember, this is the unit that will be used when you set, get, add or
+subtract brightness values.
+
 
 ### Target
 
@@ -99,50 +132,90 @@ You can choose which target to act on:
 * -l: Act on screen backlight
 * -k: Act on keyboard backlight and LEDs
 
+
 ### Field
 
-As you can not only handle the **brightness** of controllers, you may also specify a field to read/write from/to:
+As you can not only handle the **brightness** of controllers, you may
+also specify a field to read/write from/to:
 
 * -b: Current brightness of selected controller
 * -m: Maximum brightness of selected controller
 * -c: Minimum brightness (cap) of selected controller
 
-The minimum brightness is a feature implemented as some controllers make the screen go pitch black at 0%, if you have a controller like that, it is recommended to set this value (in either percent or in raw mode). These values will be saved in raw mode though, so if you specify it in percent it might not be too accurate depending on your controller.
+The minimum brightness is a feature implemented as some controllers make
+the screen go pitch black at 0%, if you have a controller like that, it
+is recommended to set this value (in percent or raw mode).  These values
+are saved in raw mode though, so if you specify it in percent it might
+not be too accurate depending on your controller.
+
 
 ### Controller modes
 
-Finally, you can either use the built-in controller selection to get the controller with the maximum precision, or you can specify one manually with the -s flag. The -a flag will force automatic mode and is default. Use -L to get a list of controllers to use with the -s flag (to specify which controller to use). 
+Finally, you can either use the built-in controller selection to get the
+controller with the maximum precision, or you can specify one manually
+with the -s flag. The -a flag will force automatic mode and is
+default. Use -L to get a list of controllers to use with the -s flag (to
+specify which controller to use).
 
-**Notice: You _need_ to include the `-s` or `-a` flag on _every_ command you run. The controller setting will _not_ be stored anywhere! If you do not use any of the flags, it will always default to automatic selection.**
+**Note:** Without the `-s` flag on _every_ command light will default
+  to automatic controller selection.
 
-### Examples
 
-Get the current brightness in percent
+Installation
+------------
 
-`light -G`, or simply `light`
+### Arch Linux
 
-Increase brightness by 5 percent
+If you run Arch Linux, there exists 2 packages;
 
-`light -A 5`
+* [light-git][] - For the absolutely latest version
+* [light-tag][] - For the latest tagged release
 
-Set the minimum cap to 2 in raw value on the acpi_video0 controller:
+We recommend you go with light-git as you might miss important features
+and bugfixes if you do not.
 
-`light -Scrs "acpi_video0" 2`
 
-Try to set the brightness to 0 after that, it will be changed to the minimum 2
+### Manual
 
-`light -Srs "acpi_video0" 0`
+We recommended downloading a versioned tarball from the relases page on
+GitHub.  Download and untar the archive:
 
-Find keyboard controllers
+    tar xf light-x.yy.tar.gz
+    cd light-x.yy/
+    ./configure && make
+    sudo make install
 
-`light -Lk`
+However, should you want to try the latest GitHub source you first need
+to clone the repository and run the `autogen.sh` script.  This requires
+`automake` and `autoconf` to be installed on your system.
 
-Activate `ScrollLock` LED
+    ./autogen.sh
+    ./configure && make
+    sudo make install
+
+The `configure` script and `Makefile.in` files are not part of GIT
+because they are generated at release time with `make release`.
 
-`light -Sks "input15::scrolllock" 100`
 
-Usually, LEDs only take 0 or 1 in raw value (i.e. for off/on), so you can write
+### Permissions
+
+**Optional:** Instead of SUID root you can set up udev rules to manage
+   sysfs permissions, you may skip the `make install` step and instead
+   copy the file `90-backlight.rules` to `/etc/udev/rules.d/`:
 
-`light -Skrs "input15::scrolllock" 1`
 
-Verify this with `light -v3 -mkrs input15::scrolllock`, you should get a max. brightness of 1
+    ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chgrp video /sys/class/backlight/%k/brightness"
+    ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chmod g+w /sys/class/backlight/%k/brightness"
+
+
+Origin & References
+-------------------
+
+Copyright (C) 2012-2018 Fredrik Haikarainen
+
+This is free software, see the source for copying conditions.  There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE
+
+[Light]:     https://github.com/haikarainen/light
+[light-git]: https://aur.archlinux.org/packages/light-git
+[light-tag]: https://aur.archlinux.org/packages/light