Add standard clone documentation. (kubevirt#943)

Signed-off-by: Alexander Wels <awels@redhat.com>

doc/clone-datavolume.md

@@ -0,0 +1,37 @@
+# How to clone an image from one DV to another one
+The purpose of this document is to show how to clone an image from an existing DV/PVC, to another DV.
+
+## Prerequisites
+- You have a Kubernetes cluster up and running with CDI installed, source DV/PVC, and at least one available PersistentVolume to store the cloned disk image.
+- The target PV is equal or larger in size than the source DV/PVC.
+- When cloning across namespaces, the user must have the ability to create pods or have 'datavolumes/source' permission in the source namespace. You can give a user the appropriate permissions to a namespace by specifying [RBAC](RBAC.md) rules.
+
+## Clone an image with DataVolume manifest
+
+Create the following DataVolume manifest [clone-datavolume.yaml](../manifest/example/clone-datavolume.yam):
+
+```yaml
+apiVersion: cdi.kubevirt.io/v1alpha1
+kind: DataVolume
+metadata:
+  name: cloned-datavolume
+spec:
+  source:
+    pvc:
+      namespace: source-ns
+      name: source-datavolume
+  pvc:
+    accessModes:
+      - ReadWriteOnce
+    resources:
+      requests:
+        storage: 500Mi
+```
+
+Deploy the DataVolume manifest:
+
+```bash
+kubectl create -f clone-datavolume.yaml
+```
+
+Two cloning pods, source and target, will be spawned and the image existed on the source DV/PVC, will be copied to the target DV.