Document DCO in CONTRIBUTING.md
This closes
@@ -17,6 +17,13 @@ Prometheus uses GitHub to manage reviews of pull requests.
Practices for Production
Environments](http://peter.bourgon.org/go-in-production/#formatting-and-style).
+* Sign your work to certify that your changes were created by yourself or you
+ have the right to submit it under our license. Read
+ https://developercertificate.org/ for all details and append your sign-off to
+ every commit message like this:
+
+ Signed-off-by: Random J Developer <example@example.com>
+
## Collector Implementation Guidelines
