update comments in _make_dataclass_serializable

Signed-off-by: mao3267 <[email protected]>

flytekit/core/type_engine.py

@@ -673,6 +673,18 @@ def _fix_structured_dataset_type(self, python_type: Type[T], python_val: typing.
     def _make_dataclass_serializable(self, python_val: T, python_type: Type[T]) -> typing.Any:
         """
         If any field inside the dataclass is flyte type, we should use flyte type transformer for that field.
+        Since other types are already serializable, this function is intended for using strings instead of directly creating Flyte files and directories in the dataclass.
+        An example shows the lifecycle:
+
+        @dataclass
+        class DC:
+            ff: FlyteFile
+
+        @task
+        def t1() -> DC:
+            return DC(ff="s3://path")
+        
+        Lifecycle: DC(ff="s3://path") -> to_literal() -> DC(ff=FlyteFile(path="s3://path")) -> msgpack -> to_python_value() -> DC(ff=FlyteFile(path="s3://path"))                                                             
         """
         from flytekit.types.directory import FlyteDirectory
         from flytekit.types.file import FlyteFile