README: Remove glib/ and subdirs from file tree
A stupid little thing, but: Since 198fdf59 there's no longer a glib/
directory on the docs-gtk-org
branch, so remove it from the directory tree shown at the top of the README.
A stupid little thing, but: Since 198fdf59 there's no longer a glib/
directory on the docs-gtk-org
branch, so remove it from the directory tree shown at the top of the README.