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/fish-deps.fish

@@ -23,6 +23,9 @@
 #
 # EXAMPLE
 #   fish-deps sync
+#   fish-deps
+#   fish-deps install
+#   fish-deps update
 function fish-deps --description 'Manage fish shell dependencies'
     set -l subcmd $argv[1]