Update network settings docs (#34848)

* doc network settings

* pylint

* pylint

sdk/ml/azure-ai-ml/azure/ai/ml/entities/_compute/compute.py

@@ -213,12 +213,13 @@ def _load_from_dict(cls, data: Dict, context: Dict, **kwargs: Any) -> "Compute":
 
 
 class NetworkSettings:
-    """Network settings for a compute resource.
+    """Network settings for a compute resource. If the workspace and VNet are in different resource groups,
+    please provide the full URI for subnet and leave vnet_name as None.
 
     :param vnet_name: The virtual network name.
-    :type vnet_name: str
+    :type vnet_name: Optional[str]
     :param subnet: The subnet name.
-    :type subnet: str
+    :type subnet: Optional[str]
 
     .. admonition:: Example: