Create configuring-queue documentation

The configuring-queue.md documentation is based on the online version
at: https://docs.cachethq.io/docs/configuring-the-queue

docs/setup/configuring-queue.md

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+# Configuring the queue
+
+Cachet uses a queue to send Configuring Mail and Beacons without slowing down
+the rest of the application. This can be setup in a variety of ways.
+
+## Supervisor
+
+The recommended setup for the queue is to use Supervisor.
+
+Supervisor is a process manager which makes managing a number of
+long-running programs a trivial task by providing a consistent interface
+through which they can be monitored and controlled.
+
+## Installations up to Cachet v2.3
+
+`cachet.conf`
+
+```
+[program:cachet-queue]
+command=php artisan queue:work --daemon --delay=2 --sleep=1 --tries=3
+directory=/var/www/cachet/
+redirect\_stderr=true
+autostart=true
+autorestart=true
+user=cachet
+```
+
+## Installations from Cachet v2.4-dev onwards
+
+`cachet.conf`
+
+```
+[program:cachet-queue]
+command=php artisan queue:work --delay=1 --sleep=1 --timeout=1800 --tries=3
+directory=/var/www/cachet/
+redirect\_stderr=true
+autostart=true
+autorestart=true
+user=cachet
+```
+
+> **Update to your configuration!**
+> Be sure to update the values in the example configuration above to match
+> your installation setup.
+
+## Database Queue with Cron
+
+The default installation of Cachet sets the queue type to database which means
+that all jobs are stored within your database and is then processed by a cron
+job which calls an artisan command from within the project directory.
+
+You'll need to create a new cron job, in Ubuntu it's a case of running
+crontab -e and adding this line:
+
+`* * * * * php /path/to/artisan schedule:run >> /dev/null 2>&1`
+
+Close the file and the cron job will now begin running, processing any
+confirmation and incident emails.
+
+## Synchronous Queue (not recommended for larger installs)
+
+If you cannot add a queue job, another alternative is to process all of
+the jobs immediately after they are created.
+
+> **Not suitable for larger installations!**
+> This setup is not ideal for larger installs with hundreds of subscribers
+> as each email can take a few seconds to send and would slow down your
+> interaction with the system.
+
+To set this up change the .env file with the following setting:
+
+`QUEUE_DRIVER=sync`