Move from doc to repo.

CONTRIBUTING.md

 ## Developer Certificate of Origin + License
 By contributing to GitLab B.V., You accept and agree to the following terms and
-conditions for Your present and future Contributions submitted to GitLab B.V. 
-Except for the license granted herein to GitLab B.V. and recipients of software 
-distributed by GitLab B.V., You reserve all right, title, and interest in and to 
-Your Contributions. All Contributions are subject to the following DCO + License 
+conditions for Your present and future Contributions submitted to GitLab B.V.
+Except for the license granted herein to GitLab B.V. and recipients of software
+distributed by GitLab B.V., You reserve all right, title, and interest in and to
+Your Contributions. All Contributions are subject to the following DCO + License
 terms.
-[DCO + License](https://docs.google.com/document/d/1HQGOMtkXU1Pipp46M5H4Un4M2xAc4D1wckTnrtii0Lo/edit)
-
+[DCO + License](https://gitlab.com/gitlab-org/dco/blob/master/README.md)
 _This notice should stay as the first item in the CONTRIBUTING.md file._