Clarify on OS disk encryption

Author: dem108

articles/machine-learning/how-to-setup-customer-managed-keys.md

@@ -41,6 +41,7 @@ In the [customer-managed keys concepts article](concept-customer-managed-keys.md
 * Resources managed by Microsoft in your subscription can’t transfer ownership to you.
 * You can't delete Microsoft-managed resources used for customer-managed keys without also deleting your workspace.
 * The key vault that contains your customer-managed key must be in the same Azure subscription as the Azure Machine Learning workspace.
+* OS disk of machine learning compute can't be encrypted with customer-managed key, but can be encrypted with Microsoft-managed key if the workspace is created with `hbi_workspace` parameter set to `TRUE`. For more details, see [Data encryption](concept-data-encryption.md#machine-learning-compute).
 * Workspace with customer-managed key doesn't currently support v2 batch endpoint.
 
 > [!IMPORTANT]