Update New-AzureADMSGroup.md

The issue below still appears to be active in version 2.0.2.140 of the AzureAD module:

https://github.com/Azure/azure-docs-powershell-azuread/issues/717

I'm updating the documentation for the parameter to clarify that the AzureADPreview module needs to be used to create dynamic groups, AzureAD does not appear to support it.

Author: PeterDeThier-MSFT

azureadps-2.0/AzureAD/New-AzureADMSGroup.md

@@ -122,8 +122,12 @@ Accept wildcard characters: False
 ```
 
 ### -GroupTypes
-Specifies that the group is a dynamic group. 
-To create a dynamic group, specify a value of DynamicMembership.
+Specifies that the group is a unified or dynamic group. 
+
+Notes: 
+
+* This parameter currently cannot be used to create dynamic groups. To create a dynamic group in PowerShell, you must use the AzureADPreview module.
+
 
 ```yaml
 Type: System.Collections.Generic.List`1[System.String]