Sorry, we don't take contributions to the main DeepVariant codebase at the moment. We expect to open the project for contributions in 1H 2018 after we configure continuous integration testing on github, formalize the external code review process, among other technical tasks to ensure that the DeepVariant codebase maintains its current high quality coding and testing standards.
In the meantime, please feel free to fork the DeepVariant codebase and prepare in your fork any patches you'd eventually like to contribute and let us know about them so we can prioritize putting the necessary infrastructure in place to accept external contributions.