Update CONTRIBUTING.md in line with...

Update CONTRIBUTING.md in line with https://about.gitlab.com/handbook/engineering/#gitlab-repositories

CONTRIBUTING.md

@@ -4,13 +4,18 @@ Thank you for your interest in contributing to this GitLab project! We welcome
 all contributions. By participating in this project, you agree to abide by the
 [code of conduct](#code-of-conduct).
 
-## Contributor license agreement
+## Developer Certificate of Origin + License
 
-By submitting code as an individual you agree to the [individual contributor
-license agreement][individual-agreement].
+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
+terms.
 
-By submitting code as an entity you agree to the [corporate contributor license
-agreement][corporate-agreement].
+[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._
 
 ## Code of conduct