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/git-clean.fish

@@ -22,6 +22,7 @@
 #
 # EXAMPLE
 #   git-clean --force
+#   git-clean
 function git-clean --description 'Sync main, prune remotes, and delete orphaned branches'
     set -l options h/help f/force
     argparse $options -- $argv