Added link to documentation about creating pull requests

CONTRIBUTING.md

@@ -9,7 +9,8 @@ For bug fixes, we will confirm that the behavior is actually a bug and that the
 is correct.  For new features, we will decide whether the proposed feature is something we
 want and discuss possible designs for it.
 
-Once everyone is in agreement, the next step is to create a pull request with the code changes.
+Once everyone is in agreement, the next step is to
+[create a pull request](https://help.github.com/en/articles/about-pull-requests) with the code changes.
 For larger features, feel free to create the pull request even before the implementaton is
 finished so as to get early feedback on the code.  When doing this, put the letters "WIP" at
 the start of the title of the pull request to indicate it is still a work in progress.