Make it clear that it's CNCF's DCO
<!--
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.
