add link to GitHub PR in build description on Jenkins

The "Details" link at the bottom of the GitHub PR page brings you to the
specific build run on Jenkins, which doesn't have a direct link back to the PR
on GitHub. We're using the description of the build to add a link back to the PR
on GitHub.

Signed-off-by: Joe Downs <joe@dwns.dev>

Author: Joe-Downs

.ci/community-jenkins/Jenkinsfile

@@ -30,6 +30,13 @@ if (buildNumber > 1) {
 }
 milestone(buildNumber)
 
+// Add build description linking back to PR. This is redundant to the "GitHub"
+// link on the Pull Request page, but the Build page does not have a direct link
+// back to the PR. The "Details" link at the bottom of the GitHub PR page brings
+// you to the Jenkins Build page, so we're adding the link back to the GitHub PR
+// page.
+currentBuild.description = "This is a build of <a href=\"${CHANGE_URL}\"}\">Open MPI PR #${CHANGE_ID}</a>"
+
 check_stages = prepare_check_stages()
 println("Initialized Pipeline")