Contributing is easy. Get a GitHub account if you don't have it already and clone this repository with the "Fork" button in the top right corner of this page. Check out your clone to your machine, code away, push your changes to your clone and submit a pull request; instructions are available at https://help.github.com/articles/fork-a-repo. (In case you need them, more detailed instructions for creating pull requests are at https://help.github.com/articles/using-pull-requests, and a basic guide to GitHub is at https://guides.github.com/activities/hello-world/.)
It's likely that we won't merge your code right away, and we'll ask for some changes instead. Don't be discouraged! That's normal; the library is complex, and thus it might take some time to become familiar with it and to use it in an idiomatic way.
We're looking forward to your contributions.