docs: Update AKS-Engine project status to deprecated

Update the project status of AKS-Engine to announce the deprecation of the project and the final version of Kubernetes that will be supported.

README.md

@@ -6,7 +6,9 @@
 
 ## Project status
 
-This project is stable, meaning the pace of new features is intentionally low. AKS Engine is maintained by teams who depend on it including [AKS Engine on Azure Stack Hub](https://docs.microsoft.com/en-us/azure-stack/user/azure-stack-kubernetes-aks-engine-overview).
+This project is deprecated for Azure public cloud customers. Please consider using [Azure Kubernetes Service (AKS)](https://azure.microsoft.com/en-us/services/kubernetes-service/#overview) for managed Kubernetes or [Cluster API Provider Azure](https://github.com/kubernetes-sigs/cluster-api-provider-azure) for self-managed Kubernetes. There are no new features planned; this project will only be updated for CVEs & similar, with Kubernetes 1.24 as the final version to receive updates.
+
+For use on [Azure Stack Hub product](https://docs.microsoft.com/en-us/azure-stack/user/azure-stack-kubernetes-aks-engine-overview) this project is fully supported until [AKS on Azure Stack Hub](https://docs.microsoft.com/en-us/azure-stack/user/aks-overview) reaches General Availability at which time it will be deprecated. AKS on Azure Stack Hub is in Public Preview as of December 2021; we encourage customers to test it.
 
 ## Overview