Merge pull request #2753 from darylyu/patch-1

Hint for CELERYBEAT_SCHEDULE args for 1-item tuple

docs/userguide/periodic-tasks.rst

@@ -131,6 +131,9 @@ Example: Run the `tasks.add` task every 30 seconds.
     please see :ref:`celerytut-configuration`.  You can either
     set these options on your app directly or you can keep
     a separate module for configuration.
+    
+    If you want to use a single item tuple for `args`, don't forget
+    that the constructor is a comma and not a pair of parentheses.
 
 Using a :class:`~datetime.timedelta` for the schedule means the task will
 be sent in 30 second intervals (the first task will be sent 30 seconds