Celery settings / readme

The backend settings state `CELERY_BACKEND = 'amqp'`. I assumed this was a shorthand for `CELERY_RESULT_BACKEND = 'amqp://`. I looked into it further because that option is [not supported](https://docs.celeryq.dev/en/stable/whatsnew-5.2.html?highlight=backend#amqp-result-backend) for Celery 5.2, but I can't actually find this configuration in the [celery docs](https://docs.celeryq.dev/en/stable/userguide/configuration.html). Perhaps this is leftover from an earlier version?

Update: Jelte mentioned you don't need to run celery during development. This could be added to the readme.