Add reference to open source image repo in readme (#397)

Co-authored-by: Michael Fu <[email protected]>

README.md

@@ -1,3 +1,7 @@
+## Note
+Starting from Airflow version 2.9, MWAA has open-sourced the original Docker image used in our production deployments. You can refer to our open-source image repository at https://github.com/aws/amazon-mwaa-docker-images to create a local environment identical to that of MWAA.
+You can also continue to use the MWAA Local Runner for testing and packaging requirements for all Airflow versions supported on MWAA.
+
 # About aws-mwaa-local-runner
 
 This repository provides a command line interface (CLI) utility that replicates an Amazon Managed Workflows for Apache Airflow (MWAA) environment locally.