Fixes #2479 (#3856)

pytorch_lightning/trainer/__init__.py

@@ -358,14 +358,15 @@ def on_train_end(self, trainer, pl_module):
 cluster_environment
 ^^^^^^^^^^^^^^^^^^^
 Environment to connect arbitrary cluster backends. Lightning automatically handles:
+
 - SLURM
 - TorchElastic
 
 For any other non-supported cluster environment, define your own class and pass it in.
 
 .. code-block:: python
 
-    from pytorch_lightning.cluster_environments import ClusterEnvironment
+    from pytorch_lightning.cluster_environments import cluster_environment
 
     class MyCluster(ClusterEnvironment):
 
@@ -378,6 +379,8 @@ def master_port(self):
         def world_size(self):
             return the_world_size
 
+    trainer = Trainer(cluster_environment=cluster_environment())
+
 default_root_dir
 ^^^^^^^^^^^^^^^^