At this time we do not plan to accept non-trivial contributions. The main purpose of this codebase is to allow the community to reproduce results from our publications.
You are however free to start a fork of the project for your purposes as permitted by the license.
Contributions to this project must be accompanied by a Contributor License Agreement (CLA). You (or your employer) retain the copyright to your contribution; this simply gives us permission to use and redistribute your contributions as part of the project. Head over to https://cla.developers.google.com/ to see your current agreements on file or to sign a new one.
You generally only need to submit a CLA once, so if you've already submitted one (even if it was for a different project), you probably don't need to do it again.
This project follows Google's Open Source Community Guidelines.