K8SPXC-1453 Added a section hor (#222)

to use dataSource
dquote>
dquote> new file:   docs/data-source.md
        modified:   mkdocs-base.yml

Author: nastena1606

Diff for: docs/data-source.md

@@ -0,0 +1,31 @@
+# Clone a cluster with the same data set
+
+A good practice is to test a new functionality or an upgraded version of the database in a testing / staging environment. As a developer, you would want the data in the staging database cluster, so that your applications can start immediately. 
+
+The [`dataSource` :octicons-link-external-16:](https://kubernetes.io/docs/concepts/storage/persistent-volumes/#volume-cloning) functionality allows doing just that. Instead of creating a new PVC for a new cluster, you can clone the existing one. This enables you to spin up a new cluster with the data in it almost in no time which is especially beneficial if you use CI/CD for that.
+
+For example, you have the production Percona XtraDB Cluster `cluster1`. To test a new feature in your app, you need a staging cluster `cluster2` with the data set from `cluster1`. 
+
+To create it, create the `cluster2-cr.yaml` Custom Resource manifest. You can use the existing [`deploy/cr.yaml` ](https://raw.githubusercontent.com/percona/percona-xtradb-cluster-operator/{{release}}/deploy/cr.yaml) for convenience. Specify the PVC from `cluster1` as the `dataSource` for it:
+
+```yaml
+pxc:
+  volumeSpec:
+    persistentVolumeClaim:
+      dataSource:
+        name: cluster1-pvc
+        kind: PersistentVolumeClaim
+
+```
+
+This configuration instructs the Operator to create a direct clone of the PVC from `cluster1`. If you have a snapshot of the PVC, you can use that as a data source for your staging cluster. Here’s how you define it:
+
+```yaml
+persistentVolumeClaim:
+  dataSource:
+    name: cluster1-pvc-snapshot1
+    kind: VolumeSnapshot
+    apiGroup: snapshot.storage.k8s.io
+```
+
+To create a database cluster, apply the `cluster2-cr.yaml`.

Diff for: mkdocs-base.yml

@@ -216,6 +216,7 @@ nav:
           - "Add sidecar containers": sidecar.md
           - "Restart or pause the cluster": pause.md
           - "Crash recovery": recovery.md
+          - data-source.md
 
     - Troubleshooting:
           - "Initial troubleshooting": debug.md