From the top README:

To clone repositories so that Ginatra can see them, clone the repositories into ./repos/ - they will be served automatically. Use the --bare switch to both save space and make sure Ginatra can read them. If you rename them, make sure the directory ends in `.git'. For Example:

cd repos
git clone --bare git://github.com/lenary/ginatra.git
git clone --bare git://github.com/mojombo/grit.git fun.git