fix spacing in checkpointing docs (#690)

Summary:
Pull Request resolved: #690

Example for loading best checkpoint wasn't displayed as code block was missing space

Reviewed By: gunchu, williamhufb

Differential Revision: D53008623

fbshipit-source-id: 3a88d67767d292883f28c1f87d0a860aa1f08cc7

docs/source/checkpointing.rst

@@ -119,6 +119,7 @@ By specifying the monitored metric to be "train_loss", the checkpointer will exp
 Later on, the best checkpoint can be loaded via
 
 .. code-block:: python
+
     TorchSnapshotSaver.restore_from_best(your_dirpath_here, unit, metric_name="train_loss", mode="min")
 
 If you'd like to monitor a validation metric (say validation loss after each eval epoch during :py:func:`~torchtnt.framework.fit.fit`), you can use the `save_every_n_eval_epochs` flag instead, like so