Mention DataAnnotations attribute as an option (dotnet#25503)

docs/standard/serialization/system-text-json-migrate-from-newtonsoft-how-to.md

@@ -4,7 +4,7 @@ description: "Learn how to migrate from Newtonsoft.Json to System.Text.Json. Inc
 author: tdykstra
 ms.author: tdykstra
 no-loc: [System.Text.Json, Newtonsoft.Json]
-ms.date: 07/21/2021
+ms.date: 08/06/2021
 zone_pivot_groups: dotnet-version
 helpviewer_keywords: 
   - "JSON serialization"
@@ -603,6 +603,8 @@ The required properties converter would require additional logic if you need to
 * A property for a non-nullable type is present in the JSON, but the value is the default for the type, such as zero for an `int`.
 * A property for a nullable value type is present in the JSON, but the value is null.
 
+**Note:** If you're using System.Text.Json from an ASP.NET Core controller, you might be able to use a [`[Required]`](xref:System.ComponentModel.DataAnnotations.RequiredAttribute) attribute on properties of the model class instead of implementing a System.Text.Json converter.
+
 ### Specify date format
 
 `Newtonsoft.Json` provides several ways to control how properties of `DateTime` and `DateTimeOffset` types are serialized and deserialized: