doc: Uses consistent Private Preview

Author: EspenAlbert

cfn-resources/resource-policy/README.md

@@ -9,7 +9,7 @@ Resource for managing [Resource Policies](https://www.mongodb.com/docs/atlas/ref
 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).
 
-**NOTE:** Resource Policies is currently in Preview, you'll need to enable `Atlas Resource Policies` Beta Feature in your organization to use it. 
+**NOTE:** Resource Policies is currently in Private Preview, you'll need to enable `Atlas Resource Policies` Beta Feature in your organization to use it. 
 
 ## Attributes and Parameters