doc: DOCSP-53434 -- Update doc for CfnCluster CDK resource

src/l1-resources/cluster/README.md

@@ -9,15 +9,15 @@ The official [MongoDB Atlas](https://www.mongodb.com/) AWS CDK resource for Node
 
 ## Description
 
-The cluster resource provides access to your cluster configurations. The resource lets you create, edit and delete clusters. The resource requires your Project ID.
+The cluster resource provides access to your cluster configurations and enable you to create, edit and delete clusters. The cluster resource requires your Project ID.
 
 ## MongoDB Atlas API Docs
 
 For more information about the API refer to: [API Endpoints](https://www.mongodb.com/docs/api/doc/atlas-admin-api-v2/group/endpoint-clusters)
 
 ## Usage
 
-In order to use this library, you will need to activate this AWS CloudFormation Registry type in your account. You can do this via the AWS Management Console or using the [AWS CLI](https://aws.amazon.com/cli/) using the following command:
+In order to use this library, you must activate the following AWS CloudFormation Registry type in your account. You can do this via the AWS Management Console or through the [AWS CLI](https://aws.amazon.com/cli/) using the following command:
 
 ```sh
 aws cloudformation activate-type \
@@ -90,6 +90,12 @@ const clusterRes = new CfnCluster(this, 'ClusterResource', {
 
 ```
 
+## Flex Clusters
+
+We now support flex clusters. See the [flex-cluster Read Me file](https://github.com/mongodb/awscdk-resources-mongodbatlas/blob/main/src/l1-resources/flex-cluster/README.md) for more details.
+
+*Note:* Although we now support flex clusters, upgrades to or from flex clusters are currently unavailable. We expect to support upgrades to or from flex clusters in the forseeable future.
+
 ## Feedback
 
 This library is auto-generated and published to all supported programming languages by the [cdklabs/cdk-cloudformation] project based on the API schema published for `MongoDB::Atlas::Cluster`.