doc: Update doc for MongoDB::Atlas::FlexCluster CFN resource (#1441)

Author: jromo-mdb

cfn-resources/flex-cluster/README.md

@@ -2,17 +2,21 @@
 
 ## Description
 
-Resource for managing [Flex Clusters](https://www.mongodb.com/docs/api/doc/atlas-admin-api-v2/group/endpoint-flex-clusters).
+The flex cluster resource provides access to your [Flex Clusters](https://www.mongodb.com/docs/api/doc/atlas-admin-api-v2/group/endpoint-flex-clusters) configurations and enables you to create, edit, and delete flex clusters. For more information, see [The MongoDB Atlas Flex Tier](https://www.mongodb.com/company/blog/product-release-announcements/dynamic-workloads-predictable-costs-mongodb-atlas-flex-tier).
+
+*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. For more information, see [`MongoDB::Atlas::Cluster` README](../cluster/README.md).
 
 ## 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
 
 See the [resource docs](docs/README.md).
 
 ## Cloudformation Examples
 
-See the examples [CFN Template](/examples/flex-cluster/flex-cluster.json) for example resource.
+See the examples [CFN Template](/examples/flex-cluster/README.md) for example resource.

examples/flex-cluster/README.md

@@ -0,0 +1,21 @@
+# How to create a MongoDB::Atlas::FlexCluster 
+
+## Step 1: Activate the cluster resource in cloudformation
+   Step a: Create Role using [execution-role.yaml](https://github.com/mongodb/mongodbatlas-cloudformation-resources/blob/master/examples/execution-role.yaml) in CFN resources folder.
+
+   Step b: Search for Mongodb::Atlas::FlexCluster resource.
+
+         (CloudFormation > Public extensions > choose 'Third party' > Search with " Execution name prefix = MongoDB " )
+   Step c: Select and activate
+         Enter the RoleArn that is created in step 1.
+
+   Your FlexCluster Resource is ready to use.
+
+## Step 2: Create template using [flex-cluster.json](flex-cluster.json)
+    Note: Make sure you are providing appropriate values for: 
+    1. ProjectId
+    2. ClusterName
+    3. BackingProviderName: AWS, GCP or AZURE
+    4. RegionName
+    5. Profile (optional)
+    6. TerminationProtectionEnabled (optional)