title: Meta.filter_overrides for IntegerRangeField in django filter view
body: <p>Using the example in the Django documentation for utilizing IntergerRangeField with Postgres backend to create ranges in "ages" with the following model:</p>
  
  <pre><code>from django.contrib.postgres.fields import IntegerRangeField
  from psycopg2.extras import NumericRange
  
  from django.db import models
  
  class Event(models.Model):
      name = models.CharField(max_length=200)
      ages = IntegerRangeField()
  
      def __str__(self):  
          return self.name
  </code></pre>
  
  <p>This works perfectly however when using Django Rest Frameworks and using filter view with the following filter:</p>
  
  <pre><code>import django_filters
  from django_filters import rest_framework as filters
  from app import Event
  
  class EventFilter(django_filters.FilterSet):
  ages = django_filters.NumericRangeFilter(queryset=Event.objects.all())
  class Meta:
      model = Event
      fields = ['name','ages']
  </code></pre>
  
  <p>the view generates an AssertionError at /api/event_filter/ and suggests adding an override to Meta.filters_override.
  What I would really appreciate is an example based on the example model for this override, the example in django-filters documentation <a href="http://django-filter.readthedocs.io/en/latest/ref/filterset.html#filter-overrides" rel="nofollow noreferrer">http://django-filter.readthedocs.io/en/latest/ref/filterset.html#filter-overrides</a>, isn't helping me understand how to get this to render.  I would appreciate any help with this so I can understand with this example to utilize this in the future.</p>