Update connect-redshift-postgresql-alloydb.md (#4489)

add iam auth info  to cloud setup to avoid user confusion.

website/docs/docs/cloud/connect-data-platform/connect-redshift-postgresql-alloydb.md

@@ -13,10 +13,12 @@ The following fields are required when creating a Postgres, Redshift, or AlloyDB
 | Port | Usually 5432 (Postgres) or 5439 (Redshift) | `5439` |
 | Database | The logical database to connect to and run queries against. | `analytics` |
 
-**Note**: When you set up a Redshift or Postgres connection in dbt Cloud, SSL-related parameters aren't available as inputs.
+**Note**: When you set up a Redshift or Postgres connection in dbt Cloud, SSL-related parameters aren't available as inputs. 
 
 <Lightbox src="/img/docs/dbt-cloud/cloud-configuring-dbt-cloud/postgres-redshift-connection.png" width="70%" title="Configuring a Redshift connection"/>
 
+For dbt Cloud users, please log in using the default Database username and password. Note this is because [`IAM` authentication](https://docs.aws.amazon.com/redshift/latest/mgmt/generating-user-credentials.html) is not compatible with dbt Cloud.
+
 ### Connecting via an SSH Tunnel
 
 To connect to a Postgres, Redshift, or AlloyDB instance via an SSH tunnel, select the **Use SSH Tunnel** option when creating your connection. When configuring the tunnel, you must supply the hostname, username, and port for the [bastion server](#about-the-bastion-server-in-aws).