Docs: Add note about version counter in ModelCheckpoint

src/lightning/pytorch/callbacks/model_checkpoint.py

@@ -95,6 +95,18 @@ class ModelCheckpoint(Checkpoint):
  If ``save_top_k >= 2`` and the callback is called multiple times inside an epoch, and the filename remains
  unchanged, the name of the saved file will be appended with a version count starting with ``v1`` to avoid
  collisions unless ``enable_version_counter`` is set to False.
+
+ .. note::
+
+ **You should not rely on the appended version to retrieve the
+ best k model**, since there is no relationship between version
+ count and model performance. For example, ``filename-v2.ckpt``
+ doesn't necessarily correspond to the 2nd best model.
+
+ The versioning is only there to prevent overwriting files. **It is recommended
+ that you pass formatting options to** ``filename``, **so the best k models can
+ be easily retrieved.** Otherwise, all checkpoints must be loaded and checked.
+
  mode: one of {min, max}.
  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.