Add a note that orchestrator return value has to be natively serializable

Author: jparta

articles/azure-functions/durable/durable-functions-serialization-and-persistence.md

@@ -155,7 +155,7 @@ For full customization of the serialization/deserialization pipeline, consider h
 
 It's recommended to use type annotations to ensure Durable Functions serializes and deserializes your data correctly. While many built-in types are handled automatically, some built-in data types require type annotations to preserve the type during deserialization.
 
-For custom data types, you make JSON serialization and deserialization possible by defining class methods `to_json` and `from_json` on your data type class.
+For custom data types, you make JSON serialization and deserialization possible by defining class methods `to_json` and `from_json` on your data type class. Note that these methods are not called on the return value from the orchestrator function, meaning the return value has to be natively JSON-serializable. For more information, see [Bindings](durable-functions-bindings.md#python-trigger-usage).
 
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