Update validation.md (dotnet#15998)

* Update validation.md

* Update validation.md

aspnetcore/mvc/models/validation.md

@@ -254,6 +254,10 @@ Notice that the `data-` attributes in the HTML output correspond to the validati
 
 Data type validation is based on the .NET type of a property, unless that is overridden by a `[DataType]` attribute. Browsers have their own default error messages, but the jQuery Validation Unobtrusive Validation package can override those messages. `[DataType]` attributes and subclasses such as `[EmailAddress]` let you specify the error message.
 
+## Unobtrusive validation
+
+For information on unobtrusive validation, see [this GitHub issue](https://github.com/aspnet/AspNetCore.Docs/issues/1111).
+
 ### Add Validation to Dynamic Forms
 
 jQuery Unobtrusive Validation passes validation logic and parameters to jQuery Validate when the page first loads. Therefore, validation doesn't work automatically on dynamically generated forms. To enable validation, tell jQuery Unobtrusive Validation to parse the dynamic form immediately after you create it. For example, the following code sets up client-side validation on a form added via AJAX.