include week in archive view

app/templates/archive.html

@@ -1,6 +1,9 @@
 {% extends "base.html" %}
 {% block content %}
     {% for item in items %}
+        {% ifchanged item.week %}
+        <h2>{{ item.year }} week {{ item.week }}</h2>
+        {% endifchanged %}
         {% include "listitem.html" with item=item %}
     {% endfor %}
 {% endblock %}