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: vim/vim#15779baee8448d1
Co-authored-by: dundargoc <gocdundar@gmail.com>