Docs did not mention default of TASK_RESULT_EXPIRES

docs/configuration.rst

@@ -1,4 +1,4 @@
-.. _configuration:
+.' _configuration:
 
 ============================
  Configuration and defaults
@@ -920,6 +920,8 @@ stored task tombstones will be deleted.
 A built-in periodic task will delete the results after this time
 (:class:`celery.task.backend_cleanup`).
 
+Default is to expire after 1 day.
+
 .. note::
 
     For the moment this only works with the amqp, database, cache, redis and MongoDB