Merge branch 'jc/doc-single-h-is-for-help' into maint

Both "git ls-remote -h" and "git grep -h" give short usage help, like any other Git subcommand, but it is not unreasonable to expect that the former would behave the same as "git ls-remote --head" (there is no other sensible behaviour for the latter). The documentation has been updated in an attempt to clarify this. * jc/doc-single-h-is-for-help: Documentation: clarify that `-h` alone stands for `help`