Don’t let them clone the public url: It doesn’t go over ssh and I don’t know how to change the origin url in a branch. *

Steps:

1. create ssh-key on new collaborators computer (ssh-keygen)
2. create github user
3. add public-key to github user account
4. let the project owner add you as project member
5. git clone git@…

Where 1 < 3, 1 < 2 < 4, 2 < 5 if that means anything to you ;-)

* it works with git remote