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/cat.fish

@@ -17,6 +17,7 @@
 #
 # EXAMPLE
 #   cat README.md
+#   cat ~/projects/myapp
 function cat --wraps='bat' --description 'Use bat for files, ls for directories, and raw cat for ANSI logs'
     # Opinionated guard (C1): fall back to bare command cat when disabled.
     if not __fish_config_op_enabled __fish_config_op_aliases