When typing `:h usr` it redirects to usr_01.txt, but I'd argue
usr_toc.txt is more useful as you can see an overview of all manuals.
When I usr `:h usr` I personally always intend to go to `usr_toc`.
closes: #15779
Signed-off-by: dundargoc <gocdundar@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>