Display postage on letter notification page

app/main/views/notifications.py

@@ -91,6 +91,7 @@ def view_notification(service_id, notification_id):
         help=get_help_argument(),
         estimated_letter_delivery_date=get_letter_timings(notification['created_at']).earliest_delivery,
         notification_id=notification['id'],
+        postage=notification['postage'],
         can_receive_inbound=(current_service.has_permission('inbound_sms')),
         is_precompiled_letter=notification['template']['is_precompiled_letter']
     )

app/templates/views/notifications/notification.html

@@ -35,6 +35,9 @@
     </p>
 
     {% if template.template_type == 'letter' %}
+      <p>
+        Sent by {{ postage }} class
+      </p>
       <p>
         Estimated delivery date: {{ estimated_letter_delivery_date|string|format_date_short }}
       </p>