Esteemed maintainers,

This is a follow-up to https://debbugs.gnu.org/cgi/bugreport.cgi?bug=43044

Despite making the man pages available, the usage text (--help) was still
not available. While `git lfs --help` did bring up the man page, `git-lfs
--help` threw 'Sorry, no usage text found for "git-lfs"'.

The attached patch fixes that. And any calls to invalid lfs commands, or
just `git-lfs` (without any sub-commands).

Thank you.