doc: DOCSP-53419 Update doc for MongoDB::Atlas::Cluster CFN resource (#1439)

Co-authored-by: Leo Antoli <430982+lantoli@users.noreply.github.com>

Author: QuiqueSanMongo

cfn-resources/cluster/README.md

@@ -1,18 +1,26 @@
-# MongoDB::Atlas::Cluster
+# MongoDB::Atlas::Cluster CFN resource
 
 ## Description
+Provides a resource for managing [Clusters](https://www.mongodb.com/docs/api/doc/atlas-admin-api-v2/group/endpoint-clusters) in AWS Cloud Formation. The resource 
+lets you create, edit, and delete clusters. The resource requires your Project 
+ID to perform these actions.
+
+*Note:* Upgrades to or from flex clusters are currently unavailable. We expect to support upgrades to or from flex clusters in the foreseeable future.
+
+*Important:* Use the `MongoDB::Atlas::Cluster` resource instead of the `MongoDB::Atlas::FlexCluster` resource to create and manage flex clusters. `MongoDB::Atlas::Cluster` supports flex clusters and future upgrades will only be available through this resource.
+
 
-Resource for managing [Clusters](https://www.mongodb.com/docs/api/doc/atlas-admin-api-v2/group/endpoint-clusters).
 
 ## Requirements
 
-Set up an AWS profile to securely give CloudFormation access to your Atlas credentials.
-For instructions on setting up a profile, [see here](/README.md#mongodb-atlas-api-keys-credential-management).
+To securely give CloudFormation access to your Atlas credentials, you must
+set up an [AWS Profile](/README.md#mongodb-atlas-api-keys-credential-management).
+
 
 ## Attributes and Parameters
+For futher information, see the [resource docs](docs/README.md) section.
 
-See the [resource docs](docs/README.md).
 
 ## Cloudformation Examples
 
-See the examples [CFN Template](/examples/cluster/cluster.json) for example resource.
+For examples, see the [CFN Template](/examples/cluster/cluster.json) example.

examples/cluster/README.md

@@ -9,7 +9,7 @@
    Step c: Select and activate
          Enter the RoleArn that is created in step 1.
 
-   Cluster Resource is ready to use.
+   Your cluster Resource is ready to use.
 
 ## Step 2: Create template using [cluster.json](project-cluster.json)
     Note: Make sure you are providing appropriate vales for