Custom Page Manager documentation fix

Thanks to @nimasmi for reporting!

docs/topics/pages.rst

@@ -473,7 +473,9 @@ Alternately, if you only need to add extra ``QuerySet`` methods, you can inherit
             today = timezone.localtime(timezone.now()).date()
             return self.filter(start_date__gte=today)
 
+    EventPageManager = PageManager.from_queryset(EventPageQuerySet)
+
     class EventPage(Page):
         start_date = models.DateField()
 
-        objects = PageManager.from_queryset(EventPageQuerySet)
+        objects = EventPageManager()