Start upgrading section in troubleshooting.md

docs/troubleshooting.md

@@ -2,6 +2,14 @@
 
 Note: `cluster$` indicates that the commands should be run as root on your OAS cluster.
 
+## Upgrading
+
+If you encounter problems when you upgrade your cluster, lease make sure first
+to include all potential new values of `ansible/group_vars/all/settings.yml.example`
+to your `clusters/YOUR_CLUSTERNAME/settings.yml`, and rerun the installation
+script.
+
+
 ## HTTPS Certificates
 
 OAS uses [cert-manager](http://docs.cert-manager.io/en/latest/) to automatically
@@ -34,4 +42,5 @@ If ever things fail beyond possible recovery, here's how to completely purge an
 
     cluster$ apt purge docker-ce-cli containerd.io
     cluster$ mount | egrep '^(tmpfs.*kubelet|nsfs.*docker)' | cut -d' ' -f 3 | xargs umount
+    cluster$ systemctl reboot
     cluster$ rm -rf /var/lib/docker /var/lib/OpenAppStack /etc/kubernetes /var/lib/etcd /var/lib/rancher /var/lib/kubelet /var/log/OpenAppStack /var/log/containers /var/log/pods