Add auto_insert_metric_name to ModelCheckpoint docstring. (#8310)

Co-authored-by: Carlos Mocholí <carlossmocholi@gmail.com>

pytorch_lightning/callbacks/model_checkpoint.py

@@ -98,6 +98,10 @@ class ModelCheckpoint(Callback):
             If ``save_top_k != 0``, the decision to overwrite the current save file is made
             based on either the maximization or the minimization of the monitored quantity.
             For ``'val_acc'``, this should be ``'max'``, for ``'val_loss'`` this should be ``'min'``, etc.
+        auto_insert_metric_name: When ``True``, the checkpoints filenames will contain the metric name.
+            For example, ``filename='checkpoint_{epoch:02d}-{acc:02d}`` with epoch 1 and acc 80 will resolve to
+            ``checkpoint_epoch=01-acc=80.ckp``. Is useful to set it to ``False`` when metric names contain ``/``
+            as this will result in extra folders.
         save_weights_only: if ``True``, then only the model's weights will be
             saved (``model.save_weights(filepath)``), else the full model
             is saved (``model.save(filepath)``).