Merge branch 'ashmckenzie/docs-ce-ee-merge-at-gitlab' into 'master'

Add section on how we run CE->EE merge at GitLab

See merge request gitlab-org/gitlab-ce!31659

doc/development/automatic_ce_ee_merge.md

@@ -171,6 +171,19 @@ Now, every time you create an MR for CE and EE:
   job failed, you are required to submit the EE MR so that you can fix the conflicts in EE
   before merging your changes into CE.
 
+## How we run the Automatic CE->EE merge at GitLab
+
+At GitLab, we use the [Merge Train](https://gitlab.com/gitlab-org/merge-train) 
+project to keep our [gitlab-ee](https://gitlab.com/gitlab-org/gitlab-ee) 
+repository updated with commits from 
+[gitlab-ce](https://gitlab.com/gitlab-org/gitlab-ce).
+
+We have a mirror of the [Merge Train](https://gitlab.com/gitlab-org/merge-train)
+project [configured](https://ops.gitlab.net/gitlab-org/merge-train) to run an 
+automatic CE->EE merge job every twenty minutes as a scheduled CI job.  The
+[configured](https://ops.gitlab.net/gitlab-org/merge-train) Merge Train project
+is only accessible to authorized GitLab staff.
+
 ## FAQ
 
 ### How does automatic merging work?