add documentation for new DCO requirements

Signed-off-by: Regina Scott <[email protected]>

Author: reginapizza

Diff for: CONTRIBUTING.md

@@ -0,0 +1,6 @@
+## Certificate of Origin
+
+By contributing to this project you agree to the Developer Certificate of
+Origin (DCO). This document was created by the Linux Kernel community and is a
+simple statement that you, as a contributor, have the legal right to make the
+contribution. Please read the [DCO text here](https://developercertificate.org/) for details.