docs: Call out strictness changes in 2.0

I'm guessing this wasn't intentional, given that it wasn't called out in
the release notes or original PR. However, 2.0 is out in the wild now so
provide a way for users to revert to the previous behavior, if they so
choose.

All of this should be integrated into a proper document, but that's a
job for another day.

Signed-off-by: Stephen Finucane <stephen@that.guru>
Fixes: 78febd1 ("Rework validation, add queryset filter method (carltongibson#788)")

docs/guide/migration.txt

@@ -82,12 +82,42 @@ FilterSet "strictness" handling moved to view (`#788`__)
 __ https://github.com/carltongibson/django-filter/pull/788
 
 Strictness handling has been removed from the ``FilterSet`` and added to the
-view layer. As a result, the ``FILTERS_STRICTNESS`` setting, ``Meta.strict``
-option, and ``strict`` argument for the ``FilterSet`` initializer have all
-been removed.
+view layer. The ``FILTERS_STRICTNESS`` setting, ``Meta.strict`` option, and
+``strict`` argument for the ``FilterSet`` initializer have all been removed.
+In addition, the default strictness has increased. A **HTTP 400** error and
+accompanying error message will be returned for invalid filters. This is
+equivalent to the ``STRICTNESS.RAISE_VALIDATION_ERROR`` setting found in 1.x.
 
 To alter strictness behavior, the appropriate view code should be overridden.
-More details will be provided in future docs.
+If using Django REST Framework, this typically means overriding
+``DjangoFilterBackend``. To provide behavior equivalent to the
+``STRICTNESS.RETURN_NO_RESULTS`` from 1.x, you should override is the backend's
+``filter_queryset`` function.
+
+.. code-block:: python
+
+    import django_filters
+    from rest_framework import exceptions
+
+    class StrictDjangoFilterBackend(django_filters.rest_framework.DjangoFilterBackend):
+        """Return no results if the query doesn't validate."""
+
+        def filter_queryset(self, request, queryset, view):
+            try:
+                return super().filter_queryset(request, queryset, view)
+            except exceptions.ValidationError:
+                return queryset.none()
+
+To provide behavior similar to ``STRICTNESS.IGNORE``, you should override the
+backend's ``raise_exception`` attribute.
+
+.. code-block:: python
+
+    import django_filters
+
+    class StrictDjangoFilterBackend(django_filters.rest_framework.DjangoFilterBackend):
+        """Ignore invalid queries."""
+        raise_exception = False
 
 
 ``Filter.name`` renamed to ``Filter.field_name`` (`#792`__)