Today I spent ages trying to create a git repository for my existing XCode projects, after much googling and trial and error I finally worked it out.
My problem was that my Mac / XCode expects git to be in /usr/bin/git so I just had to create a symlink
1) sudo ln -s /usr/local/git/bin/git /usr/bin/git
2) CD to your project folder
3) Type git init
4) Type git add .
5) Type git commit -m “Initial Commit”
6) Re open XCode and it should now be working under the newly created git repository.