(doc) Update dead link for Github PR docs

Author: Giovds

CONTRIBUTING.md

@@ -81,7 +81,7 @@ Additional Resources
 + [Apache Maven JIRA project page](https://issues.apache.org/jira/projects/MNG/)
 + [Contributor License Agreement][cla]
 + [General GitHub documentation](https://help.github.com/)
-+ [GitHub pull request documentation](https://help.github.com/send-pull-requests/)
++ [GitHub pull request documentation](https://docs.github.com/en/github/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request-from-a-fork)
 + [Apache Maven Twitter Account](https://twitter.com/ASFMavenProject)
 + #Maven IRC channel on freenode.org