Add dataSource to CSI cloning example

Author: Bob Furu

modules/persistent-storage-csi-cloning-provisioning.adoc

@@ -38,6 +38,9 @@ spec:
   resources:
     requests:
       storage: 5Gi
+  dataSource:
+    kind: PersistentVolumeClaim
+    name: pvc-1
 ----
 +
 <1> Name of the storage class that provisions the storage back end. Default storage class can be used and `storageClassName` can be omitted in the spec.