[pytorch] Update docstring for FSDP.set_state_dict_type (pytorch#103864)

Summary:
Pull Request resolved: pytorch#103864

I noticed optim_state_dict_config was missing from the Args section

Test Plan: N/A

Reviewed By: fegin, rohan-varma

Differential Revision: D46670165

fbshipit-source-id: 696fa03463e6bdecdf3ed1c38a75d1713b392f88

torch/distributed/fsdp/fully_sharded_data_parallel.py

@@ -634,6 +634,8 @@ def set_state_dict_type(
             state_dict_type (StateDictType): the desired ``state_dict_type`` to set.
             state_dict_config (Optional[StateDictConfig]): the configuration for the
                 target ``state_dict_type``.
+            optim_state_dict_config (Optional[OptimStateDictConfig]): the configuration for the optimizer state dict
+
         Returns:
             A StateDictSettings that include the previous state_dict type and
             configuration for the module.