Added some basic filtering docs

docs/filtering_sorting.rst

@@ -4,3 +4,55 @@
 Filtering And Sorting
 =====================
 
+Basic Filtering
+---------------
+
+:class:`~tastypie.resources.ModelResource` provides a basic Django ORM filter
+interface. Simply list the resource fields which you'd like to filter on and
+the allowed expression in a `filtering` property of your resource's Meta
+class::
+
+    from tastypie.constants import ALL, ALL_WITH_RELATIONS
+
+    class MyResource(ModelResource):
+        class Meta:
+            filtering = {
+                "slug": ('exact', 'startswith',),
+                "title": ALL,
+            }
+
+Valid filtering values are: Django ORM filters (e.g. ``startswith``,
+``exact``, ``lte``, etc. or the ``ALL`` or ``ALL_WITH_RELATIONS`` constants
+defined in :mod:`tastypie.constants`.
+
+These filters will be extracted from URL query strings using the same
+double-underscore syntax as the Django ORM::
+
+    /api/v1/myresource/?slug=myslug
+    /api/v1/myresource/?slug__startswith=test
+
+Advanced Filtering
+------------------
+
+If you need to filter things other than ORM resources or wish to apply
+additional constraints (e.g. text filtering using `django-haystack
+<http://haystacksearch.org>` rather than simple database queries) your
+:class:`~tastypie.resources.Resource` may define a custom
+:meth:`~tastypie.resource.Resource.build_filters` method which allows you to
+filter the queryset before processing a request::
+
+    from haystack.query import SearchQuerySet
+
+    class MyResource(Resource):
+        def build_filters(self, filters=None):
+            if filters is None:
+                filters = {}
+
+            orm_filters = super(MyResource, self).build_filters(filters)
+
+            if "q" in filters:
+                sqs = SearchQuerySet().auto_query(filters['q'])
+
+                orm_filters = {"pk__in": [ i.pk for i in sqs ]}
+
+            return orm_filters