git

download source from http://git-scm.com/

use typical_build_procedure

You can find all the documentation bundled with the Git source code in the Documentation subdirectory (the web version corresponds to the latest Git development version).

the default git build procedure will not build the documentation (man, html, etc…)

don't bother trying to do it on Mac OS X because the proper files aren't available and it is cumbersome

instead, install git as listed above, then use git to clone the latest git repo:

git clone git://git.kernel.org/pub/scm/git/git.git

at this point, the original source directory you used to build git is unnecessary

clone the git-manpages repo

git clone git://git.kernel.org/pub/scm/git/git-manpages.git

...so your directories should look like this when done:
git
git-manpages

git will install man pages to /usr/local/share/man with this, so make sure your ~/.profile has a proper MANPATH configured:

MANPATH=/usr/local/man:/usr/local/share/man:/usr/share/man
export MANPATH

cd back into the git repository, then run this to install the man pages:

sudo make prefix=/usr/local quick-install-man

you should now have proper man pages; try it with

git help status