Merge branch 'po/git-help-on-git-itself'

"git help git" was hard to discover (well, at least for some
people).

* po/git-help-on-git-itself:
Doc: git.txt: remove backticks from link and add git-scm.com/docs
git.c: show usage for accessing the git(1) help page

diff --cc Documentation/git.txt
Simple merge

diff --cc git.c
Simple merge