[Storage] Add breaking change notice for get global storage usage is obsolete

Author: blueww

src/ResourceManager/Storage/documentation/upcoming-breaking-changes.md

@@ -25,4 +25,19 @@
     https://github.com/Azure/azure-powershell/blob/dev/documentation/breaking-changes/breaking-change-template.md
 -->
 
-# Upcoming Breaking Changes
+# Upcoming Breaking Changes
+
+Release 7.0.0 - November 2018
+
+The following cmdlets were affected this release:
+
+**Get-AzureRmStorageUsage**
+- The -Location parameter changes from optional to mandatory. User must specify -Location to get Storage resource usage, since get global Storage resource usage is obsolete.
+
+```powershell
+# Old
+	$usage = Get-AzureRmStorageUsage
+
+# New
+    $usage = Get-AzureRmStorageUsage -Location $location
+    ```