Include information on updating mirror synchronization times

+ update_all_mirrors_worker_cron
+ update_all_remote_mirrors_worker_cron
+ Include source and omnibus changes

doc/workflow/repository_mirroring.md

@@ -90,5 +90,28 @@ While mirrors update once an hour, you can force an update (either **push** or
 - in the tags page
 - in the **Mirror repository** settings page
 
+## Adjusting synchronization times
+
+You can manually configure the repository synchronization times by setting the following configuration values. *These are cron formatted values.* 
+
+Please note that `update_all_mirrors_worker_cron` refers to the worker used for pulling changes from a remote mirror while `update_all_remote_mirrors_worker_cron` refers to the worker used for pushing changes to the remote mirror.
+
+**Omnibus installations**
+
+```
+# gitlab_rails['update_all_mirrors_worker_cron'] = "0 * * * *"
+# gitlab_rails['update_all_remote_mirrors_worker_cron'] = "30 * * * *"
+```
+
+**Source installations**
+
+```
+cron_jobs:
+    update_all_mirrors_worker_cron:
+      cron: "0 * * * *"
+    update_all_remote_mirrors_worker_cron:
+      cron: "30 * * * *"   
+```
+
 [ee-51]: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/51
 [perms]: ../user/permissions.md