Describe horizontal scaling support in README.md

Author: ansonj

README.md

@@ -66,6 +66,8 @@ $ bundle exec rake solid_queue:start
 
 This will start processing jobs in all queues using the default configuration. See [below](#configuration) to learn more about configuring Solid Queue.
 
+For small projects, you can run Solid Queue on the same machine as your webserver. When you're ready to scale, Solid Queue supports horizontal scaling out-of-the-box. You can run Solid Queue on a separate server from your webserver, or even run `bundle exec rake solid_queue:start` on multiple machines at the same time. If you'd like to designate some machines to be only dispatchers or only workers, use `bundle exec rake solid_queue:dispatch` or `bundle exec rake solid_queue:work`, respectively.
+
 ## Requirements
 Besides Rails 7.1, Solid Queue works best with MySQL 8+ or PostgreSQL 9.5+, as they support `FOR UPDATE SKIP LOCKED`. You can use it with older versions, but in that case, you might run into lock waits if you run multiple workers for the same queue.
 
@@ -131,7 +133,7 @@ We recommend not mixing queue order with priorities but either choosing one or t
 
 ### Threads, processes and signals
 
-Workers in Solid Queue use a thread pool to run work in multiple threads, configurable via the `threads` parameter above. Besides this, parallelism can be achieved via multiple processes, configurable via different workers or the `processes` parameter above.
+Workers in Solid Queue use a thread pool to run work in multiple threads, configurable via the `threads` parameter above. Besides this, parallelism can be achieved via multiple processes on one machine (configurable via different workers or the `processes` parameter above) or by horizontal scaling.
 
 The supervisor is in charge of managing these processes, and it responds to the following signals:
 - `TERM`, `INT`: starts graceful termination. The supervisor will send a `TERM` signal to its supervised processes, and it'll wait up to `SolidQueue.shutdown_timeout` time until they're done. If any supervised processes are still around by then, it'll send a `QUIT` signal to them to indicate they must exit.