misc: add docstring of MultiModelDDPStrategy

Author: samsara-ku

src/lightning/pytorch/strategies/ddp.py

@@ -420,6 +420,11 @@ def teardown(self) -> None:
 
 
 class MultiModelDDPStrategy(DDPStrategy):
+    """Specific strategy for training on multiple models with multiple optimizers (e.g. GAN training).
+
+    This strategy allows to wrap multiple models with DDP, rather than just one which is about just normal DDPStrategy.
+    """
+
     @override
     def _setup_model(self, model: Module) -> DistributedDataParallel:
         device_ids = self.determine_ddp_device_ids()