added message for DiskEncryptionSet identity issue

added message for DiskEncryptionSet identity issue

Author: ramankumarlive

articles/virtual-machines/windows/disk-encryption.md

@@ -99,6 +99,9 @@ The preview also has the following restrictions:
 
 1.	Grant the DiskEncryptionSet resource access to the key vault.
 
+    > [!NOTE]
+    > It may take few minutes for Azure to create the identity of your DiskEncryptionSet in your Azure Active Directory. If you get an error like "Cannot find the Active Directory object" when running the following command, wait a few minutes and try again.
+    
     ```powershell
     $identity = Get-AzADServicePrincipal -DisplayName myDiskEncryptionSet1