Added a missing import in tutorial 3.

docs/intro/tutorial03.txt

@@ -450,6 +450,8 @@ file, go ahead and add an ``app_name`` to set the application namespace:
 
     from django.conf.urls import url
 
+    from . import views
+
     app_name = 'polls'
     urlpatterns = [
         url(r'^$', views.index, name='index'),