added attachments cleanup task to example cron

misago/project_template/cron.txt

@@ -3,6 +3,7 @@
 # valid python version or paths to manage.py
 
 15 0 * * * python manage.py buildactivepostersranking
+15 0 * * * python manage.py clearattachments
 15 0 * * * python manage.py clearsessions
 15 0 * * * python manage.py invalidatebans
 15 0 * * * python manage.py prunecategories