Add video on performing a Jenkins migration
Problem to solve
We have Jenkins migration docs at https://docs.gitlab.com/ee/ci/jenkins/index.html but it's structured more as a video that someone could sit down and watch. We should do this as after completing the wrapper MVC (&2779) and use that as part of the video.
A blog post is a good step towards helping show people how easy it is to migrate from Jenkins to GitLab. We can walk people through a basic but complete Jenkins installation and how to migrate that over using tools and concepts available today.