I think the wording of this note is a bit unclear, as it doesn't clarify _which_ `__init__.py`, and doesn't really explain what it means to "ensure a particular default ...". I think it would be clearer if default_app_config were mentioned further up, right after the code block, in the main flow of the text rather than in a note. Something like:

```
You can make this AppConfig subclass the default for your app by setting ``default_app_config = "rock_n_roll.apps.RockNRollConfig"`` in ``rocknroll/__init__.py`` -- that will cause this ``AppConfig`` to be used if a user has just ``"rocknroll"`` in their INSTALLED_APPS. Alternatively, you can tell your users to put ``"rocknroll.apps.RockNRollConfig"`` in their INSTALLED_APPS.
```