Documentation: more "git-" versus "git " changes

Documentation: more "git-" versus "git " changes

With git-commands moving out of $(bindir), it is useful to make a
clearer distinction between the git subcommand 'git-whatever' and
the command you type, `git whatever <options>`.  So we use a dash
after "git" when referring to the former and not the latter.

I already sent a patch doing this same thing, but I missed some
spots.

Signed-off-by: Jonathan Nieder <jrnieder@uchicago.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>