Update returns doc

sdks/python/apache_beam/ml/inference/base.py

@@ -337,7 +337,8 @@ def load(self, key: str) -> _ModelLoadStats:
     Args:
       key: the key associated with the model we'd like to load.
     Returns:
-      the tag we can use to access the model using multi_process_shared.py.
+      _ModelLoadStats with tag, byte size, and latency to load the model. If
+        the model was already loaded, byte size/latency will be None.
     """
     # Map the key for a model to a unique tag that will persist until the model
     # is released. This needs to be unique between releasing/reacquiring th