feat: add content about vmimage backup

Signed-off-by: PoAn Yang <[email protected]>

Author: FrankYang0529

docs/vm/backup-restore.md

@@ -84,15 +84,11 @@ You can choose to either delete or retain the previous volumes. By default, all
 
 ### Restore a new VM on another Harvester cluster
 
-_Available as of v1.0.0_
+_Available as of v1.4.0_
 
 Users can now restore a new VM on another cluster by leveraging the VM metadata & content backup feature.
-
-:::info prerequisites
-
-You must manually configure the virtual machine images with the same name on the new cluster first, otherwise the virtual machines will be failed to recover.
-
-:::
+Harvester will handle VMImage data automatically. If a volume is based on a VMImage and there is a backup for it, Harvester will automatically sync the VMImage to backup target.
+In a new cluster, it the VMbackup is restored to a new VM, Harvester will automatically create the VMImage from the backup target.
 
 #### Upload the same VM images to a new cluster