Add docker image into addon conf

nextcloud_backup/config.json

@@ -33,5 +33,6 @@
     "ports": {
         "3000/tcp": 3000,
         "9226/tcp": 9226
-      }
-  }
+    },
+    "image" : "sebclemhassaddon/{arch}-hassio-nextcloud-backup"
+}