adding a preview tag

Author: yunjchoi

articles/aks/concepts-diagnostics.md

@@ -8,10 +8,12 @@ ms.date: 11/04/2019
 ms.author: yunjchoi
 ---
 
-# Azure Kubernetes Service (AKS) Diagnostics overview
+# Azure Kubernetes Service Diagnostics (preview) overview
 
 Troubleshooting Azure Kubernetes Service (AKS) cluster issues is an important part of maintaining your cluster, especially if your cluster is running mission-critical workloads. AKS Diagnostics is an intelligent, self-diagnostic experience that helps you identify and resolve problems in your cluster. AKS Diagnostics is cloud-native, and you can use it with no extra configuration or billing cost.
 
+This feature is now in public preview.
+
 ## Open AKS Diagnostics
 
 To access AKS Diagnostics: