Add missing import to tagging docs (#4158)

docs/reference/pages/model_recipes.rst

@@ -167,6 +167,8 @@ Now that we have the many-to-many tag relationship in place, we can fit in a way
 
 .. code-block:: python
     
+    from django.shortcuts import render
+
     class BlogIndexPage(Page):
         ...
         def serve(self, request):