adding description inside changelog.md

Author: hiaga

src/RecoveryServices/RecoveryServices/ChangeLog.md

@@ -20,6 +20,7 @@
 ## Upcoming Release
 * Azure Backup added a new cmdlet Copy-AzRecoveryServicesVault for DS move feature.
 * Get-AzRecoveryServicesBackupJob cmdlet now supports operation type 'BackupDataMove'.
+* Modifying the configure backup per policy limit for VMs from 100 to 1000.
 
 ## Version 2.11.1
 * Improved the Azure Backup container/item discovery experience.