Yes, it's linked at the bottom of the page:
https://github.com/kestasjk/webDiplomacy
If you're interested in contributing, we also have an issue tracker, with issues labelled as easy, medium and hard:
https://github.com/kestasjk/webDiplomacy/issues
Anything on the "soon" milestone is available to work on (though it's usually good to comment on an issue you're interested in working on first).
Instructions for developers can be found here:
http://webdiplomacy.net/developers.php
Any questions, ask me, or for longer questions, email
[email protected] and I'll reply.