README.md in fluent-plugin-aws-elasticsearch-service-2.3.0 vs README.md in fluent-plugin-aws-elasticsearch-service-2.4.0

@@ -90,9 +90,10 @@
  <endpoint>
     url https://CLUSTER_ENDPOINT_URL
     region eu-west-1
     assume_role_arn arn:aws:sts::ACCOUNT:role/ROLE
     assume_role_session_name SESSION_ID # Defaults to fluentd if omitted
+    sts_credentials_region us-west-2 # Defaults to region if omitted
   </endpoint>
 ```
 
 The policy attached to your AWS Elasticsearch cluster then becomes something like: