Added clarification about creating accounts on destination

Author: daniel-percona

readme.md

@@ -196,9 +196,10 @@ go mod tidy
 make build-local
 ```
 
-
 ## Configure Users
 
+### Migration Users
+
 You need to create users in both source and destination environments, you can name them whatever you like:
 
 ***Source (DocumentDB)***
@@ -221,6 +222,11 @@ db.getSiblingDB('admin').createUser({
   });
 ```  
 
+### Application Users
+
+Because docStreamer does not migrate user accounts or roles, you must manually create any users and roles required by your application. [Follow the appropriate procedure](https://www.mongodb.com/docs/manual/tutorial/manage-users-and-roles/) based on whether you are migrating to a sharded cluster or a replica set. Failure to create these users and roles in the destination cluster will prevent your application from connecting after the cutover process.
+
+
 ## Configuring Percona docStreamer
 
 The application is configured via the [config.yaml](./config.yaml) file in the application's root directory. You will need to at the very least edit the source and destination parameters.