record credit in CHANGELOG

Author: lonegunmanb

CHANGELOG.md

@@ -2,10 +2,4 @@
 
 ## Important Notice
 
-**This CHANGELOG.md file is no longer updated or maintained.**
-
-For the most up-to-date information about changes and updates, please refer to the
-[Release Notes](https://github.com/Azure/terraform-azurerm-aks/releases) on our GitHub releases page.
-
-The release notes contain detailed information about new features, improvements,
-bug fixes.
+* fix: add back `private_cluster_enabled` variable by @tobiasehlert [#667](https://github.com/Azure/terraform-azurerm-aks/pull/667)