Added documentation and CHANGELOG

changelogs/unreleased-ee/geo-repository-backfill-service.yml

+---
+title: Added Backfill service for Geo
+merge_request: 861
+author:

doc/gitlab-geo/README.md

@@ -69,8 +69,10 @@ there are a few things to consider:
          git remote set-url --push origin git@primary.gitlab.example.com:user/repo.git
          ```
 
-> **Important**: The initialization of a new Geo secondary node requires data
-to be copied from the primary, as there is no backfill feature bundled with it.
+>**Important**:
+The initialization of a new Geo secondary node on versions older than 8.14 
+requires data to be copied from the primary, as there is no backfill 
+feature bundled with those versions.
 See more details in the [Configure GitLab](configuration.md) step.
 
 ## Current limitations

doc/gitlab-geo/configuration.md

@@ -214,8 +214,12 @@ The two most obvious issues that replication can have here are:
 ### Step 5. Replicating the repositories data
 
 Getting a new secondary Geo node up and running, will also require the
-repositories directory to be synced from the primary node. You can use `rsync`
-for that.
+repositories directory to be synced from the primary node.
+
+With GitLab **8.14** you can start the syncing process by clicking the
+"Backfill all repositories" button on `Admin > Geo Nodes` screen. 
+
+On previous versions, you can use `rsync` for that:
 
 Make sure `rsync` is installed in both primary and secondary servers and root
 SSH access with a password is enabled. Otherwise, you can set up an SSH key-based