[ci skip] Add backend queue starting documentation

If you can't start your queue, you won't process much. This change adds external links to the Queue backends that have Active Job specific docs.

guides/source/active_job_basics.md

@@ -136,10 +136,19 @@ module YourApp
 end
 ```
 
-NOTE: Since jobs run in parallel to your Rails application, most queuing libraries
+### Starting the Backend
+
+Since jobs run in parallel to your Rails application, most queuing libraries
 require that you start a library-specific queuing service (in addition to
-starting your Rails app) for the job processing to work. For information on
-how to do that refer to the documentation of your respective library.
+starting your Rails app) for the job processing to work. Refer to library
+documentation for instructions on starting your queue backend.
+
+Here is a noncomprehensive list of documentation:
+
+- [Sidekiq](https://github.com/mperham/sidekiq/wiki/Active-Job)
+- [Resque](https://github.com/resque/resque/wiki/ActiveJob)
+- [Sucker Punch](https://github.com/brandonhilkert/sucker_punch#active-job)
+- [Queue Classic](https://github.com/QueueClassic/queue_classic#active-job)
 
 Queues
 ------