Add note on name conflict when using -v from __echo frontends

README

 NOTES
 -----
 
+ *  if when using `debug -v` you stumble on a variable name
+    that is *really* used internally by pretty.sh, routines
+    pick up the internal ones which may easily confuse you.
+    Examples are `src` or `caller`.
+
+    You can circumvent this by composing the debug string
+    yourself, e.g.:
+
+        debug "src='$src'"
+
+    in place of
+
+        debug -v src
+
+    This will be solved in the future (1.0.0?) probably by
+    refactoring the internal names to some long, ugly but
+    "safe" names.  Now, however, readability of the internal
+    code is of higher priority.
+
+    Note that there is no risk damage to data integrity, it's
+    just that the routine is unable to show you desired value.
+
+
  *  if `debug -v "x*:` is used, `x*` apparently tries to match
     *filenames* first, and only if there is no match, it goes
     on to match variable names.  This does not seem to affect