update changelog

Author: lijinpei2008

src/HealthcareApis/HealthcareApis/ChangeLog.md

@@ -18,6 +18,7 @@
         - Additional information about change #1
 -->
 ## Upcoming Release
+* Introduced various new features by upgrading code generator. Please see detail [here](https://github.com/Azure/azure-powershell/blob/main/documentation/Autorest-powershell-v4-new-features.md).
 
 ## Version 2.1.1
 * Preannounced breaking changes. Please refer to https://go.microsoft.com/fwlink/?linkid=2333229