Contributing to this project is nice and simple - fork it, make the changes and submit a Pull Request. There are only a couple of important rules you need to follow:
If you aren't civil, you will be ignored. If you continue, then you will be blocked.
If your patch makes the tests fail then it will not be immediately merged and thus might get lost.
If you update the test suite at the same time then you'll receive bonus marks and it'll also be merged quickly.
If you add new functionality, then the code won't be merged without a test showing that this new functionality works as expected.