docs(client): document gl/gL list change-symbol mappings

Add gl<sym>/gL<sym> to the lists keymap tables in README and help, noting
that 1) is command-only. Tick parity gap P1 #2.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

doc/nuwiki.txt

@@ -452,6 +452,10 @@ Lists (normal mode) ~
   gLl        Indent the item including its sublist.
   glr        Renumber the current ordered list.
   gLr        Renumber every ordered list in the buffer.
+  gl<sym>    Set the current item's marker to <sym>, where <sym> is one
+             of `-` `*` `#` `1` (1.) `i` (i)) `I` (I)) `a` (a)) `A` (A)).
+             For `1)` use `:NuwikiChangeSymbol 1)` (no single-key form).
+  gL<sym>    Set every item in the list to <sym> (same symbol keys).
   gl<Space>  Remove every completed item from the current list.
   gL<Space>  Remove every completed item in the buffer.
   o          Open a new line and continue the list marker (preserves