[Storage] Update Change log for add warning message of get global usage obsolete

Author: blueww

src/ResourceManager/Storage/Commands.Management.Storage/ChangeLog.md

@@ -1,4 +1,4 @@
-<!--
+,<!--
     Please leave this section at the top of the change log.
 
     Changes for the current release should go under the section titled "Current Release", and should adhere to the following format:
@@ -18,7 +18,7 @@
         - Additional information about change #1
 -->
 ## Current Release
-* Support get the Storage resource usage of a specific location
+* Support get the Storage resource usage of a specific location, and add warning message for get global Storage resource usage is obsolete.
     - Get-AzureRmStorageUsage
 
 ## Version 5.1.0