Update gitlab_flow.md to add GitLab Flow video

doc/workflow/gitlab_flow.md

@@ -27,6 +27,8 @@ People have a hard time figuring out which branch has the latest code, or which
 Frequently, the reaction to this problem is to adopt a standardized pattern such as [Git flow](https://nvie.com/posts/a-successful-git-branching-model/) and [GitHub flow](http://scottchacon.com/2011/08/31/github-flow.html).
 We think there is still room for improvement. In this document, we describe a set of practices we call GitLab flow.
 
+For a video introduction of how this works in GitLab, see [GitLab Flow](https://youtu.be/InKNIvky2KE).
+
 ## Git flow and its problems
 
 ![Git Flow timeline by Vincent Driessen, used with permission](gitdashflow.png)