Added docstring to explain serialization

ludwig/hyperopt/syncer.py

@@ -33,8 +33,9 @@ def _delete_command(self, uri: str) -> Tuple[Callable, Dict]:
                 dict(uri=uri),
             )
 
-    # Custom deserialization needed since we can't pickle thread.lock objects
     def __reduce__(self):
+        """We need this custom serialization because we can't pickle thread.lock objects that are used by the
+        use_credentials context manager."""
         deserializer = RemoteSyncer
         serialized_data = (self.sync_period, self.backend)
         return deserializer, serialized_data