Add note about zipfile format in serialization tutorial

Author: James Reed

beginner_source/saving_loading_models.py

@@ -156,6 +156,12 @@
 #    model.load_state_dict(torch.load(PATH))
 #    model.eval()
 #
+# .. note::
+#     The 1.6 release of PyTorch switched ``torch.save`` to use a new
+#     zipfile-based file format. ``torch.load`` still retains the ability to
+#     load files in the old format. If for any reason you want ``torch.save``
+#     to use the old format, pass the kwarg ``_use_new_zipfile_serialization=False``.
+#
 # When saving a model for inference, it is only necessary to save the
 # trained model’s learned parameters. Saving the model’s *state_dict* with
 # the ``torch.save()`` function will give you the most flexibility for