chore: add note about Postgres-only IAM DB Authn (#116)

* chore: add note about Postgres-only IAM DB Authn

* chore: update docstring

Author: enocom

README.md

@@ -112,7 +112,8 @@ connector.connect(
 Note: If specifying Private IP, your application must already be in the same VPC network as your Cloud SQL Instance. 
 
 ### IAM Authentication
-Connections using [IAM database authentication](https://cloud.google.com/sql/docs/postgres/iam-logins) are supported when using the Postgres driver. 
+Connections using [IAM database authentication](https://cloud.google.com/sql/docs/postgres/iam-logins) are supported when using the PostgreSQL driver.
+This feature is unsupported for other drivers.
 First, make sure to [configure your Cloud SQL Instance to allow IAM authentication](https://cloud.google.com/sql/docs/postgres/create-edit-iam-instances#configure-iam-db-instance) and [add an IAM database user](https://cloud.google.com/sql/docs/postgres/create-manage-iam-users#creating-a-database-user). 
 Now, you can connect using user or service account credentials instead of a password. 
 In the call to connect, set the `enable_iam_auth` keyword argument to true and `user` to the email address associated with your IAM user.

google/cloud/sql/connector/connector.py

@@ -75,7 +75,7 @@ def connect(
         can be either IPTypes.PUBLIC or IPTypes.PRIVATE.
 
     :param enable_iam_auth
-        Enables IAM based authentication for Postgres instances.
+    Enables IAM based authentication (PostgreSQL only).
     :type enable_iam_auth: bool
 
     :param kwargs: