Add Backup instructions

Closes: #152

docs/index.rst

@@ -28,6 +28,7 @@ For more information, go to `the OpenAppStack website`_.
 
    installation_instructions
    testing_instructions
+   troubleshooting
+   maintenance
    design
    reference
-   troubleshooting

docs/maintenance.md

+# Maintaining an Openappstack cluster
+
+## Backup
+
+Please take care to backup the following locations:
+
+### On your provisioning machine
+
+* Your cluster config directory where you put your `inventory.yml` and
+  `settings.yml` files. This is also the place where the generated secrets
+  are stored during installation. It's located under at `openappstack/clusters`
+
+### On your cluster
+
+* The local storage directories under `/var/lib/OpenAppStack/local-storage`.
+  This is the place all persistant volumes are stored.
+  Some are more important than others, if you want to hand-pick what volumes
+  to backup, use `kubectl get pvc --all-namespaces` to see which volumes are
+  used by what application. The prometheus volumes usually take the most space
+  for retaining metrics.
+  We recommend backing up the whole directory.
+* The [rke](https://rancher.com/docs/rke/latest/en/) directory `/var/lib/OpenAppStack/rke`
+  where the `rke` config and state file of your cluster is stored.
+* At this moment, [recurring, automated etcd snapshots are not configured](https://open.greenhost.net/openappstack/openappstack/issues/453).
+  Please refer to the [rke etc snapshot
+  documentation](https://rancher.com/docs/rke/latest/en/etcd-snapshots/) if you
+  like to backup [etcd](https://etcd.io/).
+
+If you don't care about your backup disk usage too much, the easiest way is to
+backup the whole `/var/lib/OpenAppStack/` directory.
+
+## Restore
+
+Restore instructions will follow, please reach out to us if you need assistance.