Make it clear that it's CNCF's DCO

Signed-off-by: Richard Hartmann <richih@richih.org>

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,7 +1,7 @@
 <!--
     Don't forget!
 
-    - Sign your commits and our DCO:  https://docs.github.com/en/github/authenticating-to-github/managing-commit-signature-verification/signing-commits
+    - Please sign CNCF's Developer Certificate of Origin and sign-off your commits by adding the -s / --sign-off flag to `git commit`. See https://github.com/apps/dco for more information.
 
     - If the PR adds or changes a behaviour or fixes a bug of an exported API it would need a unit/e2e test.