Add documentation about transition from placementRule to placement

Ref: https://issues.redhat.com/browse/ACM-12698
Signed-off-by: yiraeChristineKim <yikim@redhat.com>

README.md

@@ -99,6 +99,68 @@ For additional information about the Policy Generator:
 - [Policy Generator reference YAML](https://github.com/stolostron/policy-generator-plugin/blob/main/docs/policygenerator-reference.yaml)
 - [Policy Generator examples](policygenerator)
 
+## Transition from PlacementRule to Placement
+### Prerequisite
+- [ManagedClusterSet](https://open-cluster-management.io/concepts/managedclusterset/) and [ManagedClusterSetBinding](https://open-cluster-management.io/concepts/managedclusterset)
+- `Policy`(The `namespace` in the `policy` should be bound to `ManagedClusterSetBinding`)
+- `PlacementBinding` and `PlacementRule`
+```yaml
+apiVersion: policy.open-cluster-management.io/v1
+kind: PlacementBinding
+metadata:
+  name: binding-policy-comp-operator
+placementRef:
+  name: placement-policy-comp-operator
+  kind: PlacementRule
+  apiGroup: apps.open-cluster-management.io
+subjects:
+  - name: policy-comp-operator
+    kind: Policy
+    apiGroup: policy.open-cluster-management.io
+---
+apiVersion: apps.open-cluster-management.io/v1
+kind: PlacementRule
+metadata:
+  name: placement-policy-comp-operator
+spec:
+  clusterSelector:
+    matchExpressions:
+      - {key: vendor, operator: In, values: ["OpenShift"]}
+```
+
+## Convert PlacementRule to Placement
+Create the `Placement` manifest as shown below. This `Placement` manifest replaces the `PlacementRule`. Ensure that the `namespace` specified (`comp-operator-ns`) matches the `namespace` used in `ManagedClusterSetBinding`. Copy `matchExpressions` from the `PlacementRule` and paste them into `spec.predicates.requiredClusterSelector.labelSelector`. Update the `PlacementBinding` to reference the new `Placement`. Change the `placementRef.kind` to `Placement` and update the `placementRef.apiGroup` to `cluster.open-cluster-management.io` to reflect the `Placement`'s API version.
+```yaml
+apiVersion: cluster.open-cluster-management.io/v1beta1
+kind: Placement
+metadata:
+  name: placement-policy-comp-operator
+  namespace: comp-operator-ns // Please ensure that this namespace matches one in ManagedClusterSetBinding
+spec:
+  predicates:
+  - requiredClusterSelector:
+      labelSelector:
+        matchExpressions: // From PlacementRule
+         - {key: vendor, operator: In, values: ["OpenShift"]} 
+---
+apiVersion: policy.open-cluster-management.io/v1
+kind: PlacementBinding
+metadata:
+  name: binding-policy-comp-operator
+placementRef:
+  name: placement-policy-comp-operator
+  kind: Placement // Set here to Placement
+  apiGroup: cluster.open-cluster-management.io // Set cluster.open-cluster-management.io
+subjects:
+  - name: policy-comp-operator
+    kind: Policy
+    apiGroup: policy.open-cluster-management.io
+```
+
+For more details on Placement, refer to the [Placement concept](https://open-cluster-management.io/concepts/placement/) documentation. 
+
+This explanation provides a clear transition from using `PlacementRule` to `Placement`, ensuring compatibility and proper configuration alignment with Open Cluster Management principles.
+
 ## Community, discussion, contribution, and support
 
 Check the [Contributing policies](CONTRIBUTING.md) document for guidelines on how to contribute to
@@ -111,3 +173,5 @@ are implemented in the product governance framework.
 
 - [Open Cluster Management Quick Start](https://https://open-cluster-management.io/getting-started/quick-start/)
 
+
+