Add variable docstrings where missing

src/saturnin.sh.skel

     # In such cases, it makes sense to print also version information to
     # help users with reporting.
     #
-    local msg
+    local msg           # message core
     for msg in "$@";
     do
         warn "bug: $msg"
     # This is aimed to help debugging and testing the app (or Saturnin
     # itself) by showing packaging and deployment related info.
     #
-    local key=${1#--saturnin-get-}
+    local key=${1#--saturnin-get-}      # internal info key
     case "$key" in
         saturnin-conf-path) echo "$SATURNIN_CONF_PATH"      ;;
         app-git-hash)   echo "$SATURNIN_APP_GIT_HASH"       ;;
     # After setting all mandatory environment variables, call this from your
     # main meta-command script.
     #
-    local subcommand
+    local subcommand    # subcommand to execute (first non-option)
     test -n "$SATURNIN_CACHE_HOME"     || die "SATURNIN_CACHE_HOME is not set"
     test -n "$SATURNIN_LIBEXEC"        || die "SATURNIN_LIBEXEC is not set"
     test -n "$SATURNIN_LIBEXEC_PREFIX" || die "SATURNIN_LIBEXEC_PREFIX is not set"
     # unless syntax check fails, execute it as Bash code (in separate
     # process).
     #
-    local hname="$1"
-    local hook_code
+    local hname="$1"    # hook name
+    local hook_code     # ... code
     test -n "$SATURNIN_SUBCOMMAND" || {
         warn "unknown subcommand, ignoring hook: $hname"
         return 0
     # status of the payload command, even if hooks fail.  Ignore post-hook
     # if payload command failed.
     #
-    local es=0
+    local es=0      # exit status of thid function
     saturnin__runhook pre
     "$@" || return $?
     es=$?
     # drop them and also get the colons right.
     #
     local idx=0     # current item index (zero-based)
-    local path
+    local path      # each path on stdin
     while read -r path;
     do
         test -z "$path" && continue