docs(functions): merge manual-only examples and notes into headers

Folds the examples Section 5 carried but the headers did not into each
function's `# EXAMPLE`, and moves the three lines that only looked like
examples -- the two typo-abbreviation notes and rm's /usr/bin/rm fallback --
into `# NOTES`, the label already in use.

Also corrects gi's synopsis, which omitted -l, and documents yt-dlp's
--no-embed-thumbnail in `# ARGUMENTS`.

functions/rg.fish

@@ -17,6 +17,8 @@
 #
 # EXAMPLE
 #   rg "TODO" src/
+#   rg "fish_greeting" ~/.config/fish/
+#   rg -l "TODO" ~/projects/myapp
 function rg --description 'alias rg=rg --hyperlink-format=kitty'
     # Opinionated guard (C1): fall back to bare command rg when disabled.
     if not __fish_config_op_enabled __fish_config_op_aliases