Update policy-for-kubernetes.md

Updated documentation to reflect that built in definitions and custom definitions are both offered for Azure Policy for Kubernetes definitions

Author: nehakulkarni123

articles/governance/policy/concepts/policy-for-kubernetes.md

@@ -51,8 +51,6 @@ The following general limitations apply to the Azure Policy Add-on for Kubernete
 
 - Azure Policy Add-on for Kubernetes is supported on Kubernetes version **1.14** or higher.
 - Azure Policy Add-on for Kubernetes can only be deployed to Linux node pools.
-- Only built-in policy definitions are supported. Custom policy definitions are a _public preview_
-  feature.
 - Maximum number of pods supported by the Azure Policy Add-on: **10,000**
 - Maximum number of Non-compliant records per policy per cluster: **500**
 - Maximum number of Non-compliant records per subscription: **1 million**