Add missing newline to the Jenkins integration doc

A prior commit (b05a7249) accidentally
removed a newline separating the paragraphs about the integration video
and the list of when to use the integration

doc/integration/jenkins.md

@@ -18,6 +18,7 @@ on the GitLab project's home page.
 To better understand GitLab's Jenkins integration, watch the following video:
 
 - [GitLab workflow with Jira issues and Jenkins pipelines](https://youtu.be/Jn-_fyra7xQ)
+
 Use the Jenkins integration with GitLab when:
 
 - You plan to migrate your CI from Jenkins to [GitLab CI/CD](../ci/README.md) in the future, but