mention evaluation steps in TSS docs (#657)

Summary:
Pull Request resolved: #657

Mention that training **and** evaluation steps are combined when forming the checkpoint name

Reviewed By: galrotem

Differential Revision: D52224894

fbshipit-source-id: 4545486bc8e19a3a3336752f053db2c3fa474a4e

torchtnt/framework/callbacks/torchsnapshot_saver.py

@@ -60,7 +60,7 @@ class TorchSnapshotSaver(BaseCheckpointer):
 
     If used with :func:`torchtnt.framework.fit`, this class will also save the evaluation progress state.
 
-    Checkpoints will be saved under ``dirpath/epoch_{epoch}_step_{step}`` where step is the *total* number of training steps completed across all epochs.
+    Checkpoints will be saved under ``dirpath/epoch_{epoch}_step_{step}`` where step is the *total* number of training and evaluation steps completed across all epochs.
 
     Args:
         dirpath: Parent directory to save snapshots to.