Specify behaviour of a process with no queue option set

Closes #425.

README.md

@@ -220,6 +220,12 @@ Configured queue priorities can be overriden by passing priority to the delay me
 object.delay(:queue => 'high_priority', priority: 0).method
 ```
 
+You can start processes to only work certain queues with the `queue` and `queues`
+options defined below. Processes started without specifying a queue will run jobs
+from **any** queue. To effectively have a process that runs jobs where a queue is not
+specified, set a default queue name with `Delayed::Worker.default_queue_name` and 
+have the processes run that queue.
+
 Running Jobs
 ============
 `script/delayed_job` can be used to manage a background process which will