docs: add docs for volumegroupreplication CR

add docs for volumegroupreplication and volumegroupreplicationclass
CRs.

Signed-off-by: Nikhil-Ladha <nikhilladha1999@gmail.com>

Author: Nikhil-Ladha

docs/volumegroupreplicationclass.md

@@ -0,0 +1,24 @@
+# VolumeGroupReplicationClass
+
+VolumeGroupReplicationClass is a cluster scoped resource that contains driver related configuration parameters for volume group replication.
+
+`provisioner` is name of the storage provisioner.
+
+`parameters` contains key-value pairs that are passed down to the driver. Users can add their own key-value pairs. Keys with `replication.storage.openshift.io/` prefix are reserved by operator and not passed down to the driver.
+
+## Reserved parameter keys
+
+- `replication.storage.openshift.io/group-replication-secret-name`
+- `replication.storage.openshift.io/group-replication-secret-namespace`
+
+```yaml
+apiVersion: replication.storage.openshift.io/v1alpha1
+kind: VolumeGroupReplicationClass
+metadata:
+  name: volumegroupreplicationclass-sample
+spec:
+  provisioner: example.provisioner.io
+  parameters:
+    replication.storage.openshift.io/group-replication-secret-name: secret-name
+    replication.storage.openshift.io/group-replication-secret-namespace: secret-namespace
+```