Point Django attendees to contributing guide

The GitHub page isn't a great start, the contributing guide is where to go to begin with!

Also, I'll be there! :)

Author: adamchainz

_posts/2018-11-14-django.md

@@ -23,5 +23,5 @@ No matter if this is your first sprint or if you are a seasoned sprinter with us
 Remember to:
 
 - Bring your own charged laptop
-- Check out the [Django GitHub](https://github.com/django/django) if you want to get an early start.
+- Check out the [Django Contributing Guide](https://docs.djangoproject.com/en/dev/internals/contributing/) if you want to get an early start.
 - Join the [Gitter channel](https://gitter.im/py-sprints/django) of the sprint