ValveSoftware/source-sdk-2013 — pull request #12 by johndrinkwater (2013-06-27 18:11:44+00:00)
Title: Add CONTRIBUTING file

To better manage copyright assignment (and reduce back & forths on pull requests as seen in https://github.com/ValveSoftware/source-sdk-2013/commit/823818305dd9e4712c9bea17e80ead3c1b52fd3f#commitcomment-3520133) put a statement in CONTRIBUTING about the requirement, a common repo file to specify how to contribute.
IANAL, but this should do.