Update to README.md to include LZA Notice (#1105)

Author: archikierstead

README.md

@@ -1,3 +1,11 @@
+# ATTENTION
+
+The [Landing Zone Accelerator (LZA) on AWS solution](https://aws.amazon.com/solutions/implementations/landing-zone-accelerator-on-aws/) is now the recommended solution for organizations seeking to automate the deployment of a new high compliance AWS Environment.
+
+The LZA v1.3 release focused on delivering AWS Secure Environment Accelerator (ASEA) feature parity and delivered both [CCCS Cloud Medium](https://docs.aws.amazon.com/solutions/latest/landing-zone-accelerator-on-aws/canadian-centre-for-cyber-security-cccs-cloud-medium.html) and [Trusted Secure Enclave Sensitive Edition](https://docs.aws.amazon.com/solutions/latest/landing-zone-accelerator-on-aws/trusted-secure-enclaves-sensitive-edition-for-national-security-defence-and-national-law-enforcement.html) sample configuration files.  These samples deliver similar outcomes to the ASEA sample configuration file.
+
+The LZA team is currently developing a semi-automated upgrade from ASEA to LZA. If you are using the ASEA, there is currently no deadline to migrate to the Landing Zone Accelerator on AWS solution.  Please reach out to your AWS Account Team with any questions.
+
 # AWS Secure Environment Accelerator
 
 The AWS Accelerator is a tool designed to help deploy and operate secure multi-account, multi-region AWS environments on an ongoing basis. The power of the solution is the configuration file that drives the architecture deployed by the tool. This enables extensive flexibility and for the completely automated deployment of a customized architecture within AWS without changing a single line of code.