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/mkcd.fish

@@ -24,6 +24,7 @@
 #
 # EXAMPLE
 #   mkcd ~/projects/myapp
+#   mkcd ~/projects/newapp/src
 function mkcd --description 'Create a directory (with parents) and cd into it'
     set -l c_head (set_color --bold cyan)
     set -l c_cmd  (set_color --bold white)