Updated documentation settings for DatabaseScheduler.

[rh0dium]

Checklist

• I have included the output of celery -A proj report in the issue.
  (if you are not able to do this, then at least specify the Celery
  version affected).
• I have verified that the issue exists against the master branch of Celery.

celery -A celery_app report
/Users/sklass/.virtualenvs/icm_ipcatalog/lib/python2.7/site-packages/django/conf/__init__.py:122: RemovedInDjango110Warning: Session verification will become mandatory in Django 1.10. Please add 'django.contrib.auth.middleware.SessionAuthenticationMiddleware' to your MIDDLEWARE_CLASSES setting when you are ready to opt-in after reading the upgrade considerations in the 1.8 release notes.
  RemovedInDjango110Warning

software -> celery:4.0.2 (latentcall) kombu:4.0.2 py:2.7.10
            billiard:3.5.0.2 py-amqp:2.1.4
platform -> system:Darwin arch:64bit imp:CPython
loader   -> celery.loaders.app.AppLoader
settings -> transport:amqp results:django-db

Steps to reproduce

1. If you use the suggested settings in the documents this will create the django.db file which is in alignment with the docs.
2. However the scheduler is incorrect.

Expected behavior

1. Change the docs so the Django.db is not created and the right scheduler is used.

Actual behavior

Reference: celery/django-celery-beat#48