add SMC article link

Author: arkogupta

docs/declarative-customization/formatting-syntax-reference.md

@@ -365,8 +365,9 @@ See [here](./column-formatting.md#formatting-multi-value-fields) for examples.
       }
     }
     ```
-    
-- **embed**: Clicking on the button will open a callout with content embedded in it. The content will be determined by the URL provided in the `src` attribute in `actionInput`. You can also control the `height` and `width` of the callout using the actionInput. Note that the src has to be just the url part of an embeddable code generated by an app.
+
+- **embed**: Clicking on the button will open a callout with content embedded in it. The content will be determined by the URL provided in the `src` attribute in `actionInput`. You can also control the `height` and `width` of the callout using the actionInput. Note that the src has to be just the url part of an embeddable code generated by an app.\
+Refer to this article for more information about how to allow list domains - https://support.microsoft.com/en-us/office/allow-or-restrict-the-ability-to-embed-content-on-sharepoint-lists-using-custom-formatters-276bad2e-4639-452e-af12-f860313b9f63.\
 Note - This action is only available in the newer version of the Microsoft Lists App.
 
     ```JSON