Update preview-features.md

Adding instructions for configuring Preview Features using Azure Policy.

Author: ifeoluwaokunoren

articles/azure-resource-manager/management/preview-features.md

@@ -345,6 +345,8 @@ InGuestPatchVMPreview   Microsoft.Compute   Unregistered
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+## Configuring Preview Features using Azure Policy
+Subscriptions can be remediated to register to a preview feature if not already registered using a [built-in](https://portal.azure.com/#blade/Microsoft_Azure_Policy/PolicyDetailBlade/definitionId/%2Fproviders%2FMicrosoft.Authorization%2FpolicyDefinitions%2Fe624c84f-2923-4437-9fd9-4115c6da3888) definition. Please note that new subscriptions added to an existing tenant will not be automatically registered.
 
 ## Next steps