Announce upcoming Azure Batch breaking changes

Author: matthchr

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

@@ -25,4 +25,15 @@
     https://github.com/Azure/azure-powershell/blob/dev/documentation/breaking-changes/breaking-change-template.md
 -->
 
-# Upcoming Breaking Changes
+# Upcoming Breaking Changes
+
+## Release 5.0.0
+
+The following cmdlets were affected this release:
+
+**Get-AzureBatchTaskCounts**
+ - The `Microsoft.Azure.Commands.Batch.Models.PSTaskCounts` model returned by this cmdlet has had the `ValidationStatus` property
+   removed.
+
+**Add-AzureBatchPool**
+ - The `Caching` default for `Microsoft.Azure.Commands.Batch.Models.PSDataDisk` is now `ReadWrite` instead of `None`.