docs: backup: Fix missing volume creation

* Create the volume before extracting.
* Resolves #195

Author: kylemanna

docs/backup.md

@@ -13,8 +13,9 @@ I'd recommend encrypting the archive with something strong (e.g. gpg or openssl
 
     docker run -v $OVPN_DATA:/etc/openvpn --rm kylemanna/openvpn tar -cvf - -C /etc openvpn | xz > openvpn-backup.tar.xz
 
-## Restore to New Container
+## Restore to New Data Volume
 
-Assumes an existing container named `$OVPN_DATA` to extract the data over the top.
+Creates an volume container named `$OVPN_DATA` to extract the data to.
 
-    xzcat openvpn-backup.tar.xz | docker run --name $OVPN_DATA -v /etc/openvpn -i kylemanna/openvpn tar -xvf - -C /etc
+    docker volume create --name $OVPN_DATA
+    xzcat openvpn-backup.tar.xz | docker run $OVPN_DATA:/etc/openvpn -i kylemanna/openvpn tar -xvf - -C /etc