Add a new configuration to tests the training command

Would have been useful for this dev: !299 (merged) because tox doesn't test everything and we sometimes have to run the command ourselves.

docs/get_started/development.md

@@ -26,7 +26,9 @@ tox
 
 To recreate tox virtual environment (e.g. a dependencies update), you may run `tox -r`.
 
-### Train command
+### Commands
+
+As unit tests do not test *everything*, it is sometimes necessary to use DAN commands directly to test developments.
 
 The library already has all the documents needed to run the [training command](../usage/train/index.md) on a minimalist dataset. You can use the configuration available at `configs/tests.json`. It is already populated with the parameters used in the unit tests.