docs: small improvment in backup

Just a small addition to help user during backup configuration.

Signed-off-by: Loic Devulder <ldevulder@suse.com>

docs/backup.md

@@ -164,7 +164,7 @@ Then apply changes to Kubernetes cluster
 kubectl apply -f rancher-resource-set.yaml
 ```
 
-Create backup with creating Backup object
+Create `elemental-backup.yaml` file which allows backup with creating Backup object
 
 ```yaml showLineNumbers
 apiVersion: resources.cattle.io/v1
@@ -177,6 +177,12 @@ spec:
   retentionCount: 10
 ```
 
+Then apply changes to Kubernetes cluster
+
+```shell showLineNumbers
+kubectl apply -f elemental-backup.yaml
+```
+
 Check logs from rancher-backup operator
 
 ```shell showLineNumbers