This also adds the DEFAULT_AUTO_FIELD to the app's Django settings to
resolve this warning when running `migrate`:
```
ingredients.Category: (models.W042) Auto-created primary key used when not defining a primary key type, by default 'django.db.models.AutoField'.
HINT: Configure the DEFAULT_AUTO_FIELD setting or the IngredientsConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.
```
Currently the relay cookbook's readme has a link to the plain tutorial
page. The plain cookbook readme also instructs the user to change
directory into the directory for the relay example. This change fixes
both issues.
Also changed the title for the relay example to specify that it uses
relay.
