All contributions (including pull requests) must agree to the Developer Certificate of Origin (DCO) version 1.1. This is exactly the same one created and used by the Linux kernel developers and posted on http://developercertificate.org/. This is a developer's certification that he or she has the right to submit the patch for inclusion into the project. Simply submitting a contribution implies this agreement, however, please include a "Signed-off-by" tag in every patch (this tag is a conventional way to confirm that you agree to the DCO).