Add a note about passthrough mounts and service principals (#1140)

Author: alexott

docs/resources/mount.md

@@ -56,6 +56,8 @@ resource "databricks_mount" "this" {
 
 ### Example mounting ADLS Gen2 with AAD passthrough
 
+**Note** You can't create AAD passthrough mount using service principal!
+
 To mount ALDS Gen2 with Azure Active Directory Credentials passthrough we need to execute the mount commands using the cluster configured with AAD Credentials passthrough & provide necessary configuration parameters (see [documentation](https://docs.microsoft.com/en-us/azure/databricks/security/credential-passthrough/adls-passthrough#--mount-azure-data-lake-storage-to-dbfs-using-credential-passthrough) for more details).
 
 ```hcl