doc: DCO anchor that doesn't change

PR-URL: #6257
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: williamkapke

CONTRIBUTING.md

@@ -173,6 +173,7 @@ to address, apply your changes in a separate commit and push that to your
 feature branch. Post a comment in the pull request afterwards; GitHub does
 not send out notifications when you add commits.
 
+<a id="developers-certificate-of-origin"></a>
 ## Developer's Certificate of Origin 1.1
 
 By making a contribution to this project, I certify that: