Upgrade guide: what setting WEB_CONCURRENCY does

This is what happened in puma#2143.

5.0-Upgrade.md

@@ -84,12 +84,12 @@ To learn more about using `refork` and `fork_worker`, see ['Fork Worker'](docs/f
 
 ## Upgrade
 
-* Setting the `WEB_CONCURRENCY` environment variable will now configure the number of workers (processes) that Puma will boot.
+* Setting the `WEB_CONCURRENCY` environment variable will now configure the number of workers (processes) that Puma will boot and enable preloading of the application.
 * If you did not explicitly set `environment` before, Puma now checks `RAILS_ENV` and will use that, if available in addition to `RACK_ENV`.
 * If you have been using the `--control` CLI option, update your scripts to use `--control-url`.
 * If you are using `worker_directory` in your config file, change it to `directory`.
 * If you are running MRI, default thread count on Puma is now 5, not 16. This may change the amount of threads running in your threadpool. We believe 5 is a better default for most Ruby web applications on MRI. Higher settings increase latency by causing GVL contention.
-* If you are using a worker count of more than 1, Puma will now preload the application by default (disable with `preload_app! false`). We believe this is a better default, but may cause issues in non-Rails applications if you do not have the proper `before` and `after` fork hooks configured. See documentation for your framework. Rails users do not need to change anything. **Please note that it is not possible to use [the phased restart](docs/restart.md) with preloading.**
+* If you are using a worker count of more than 1, set using `WEB_CONCURRENCY`, Puma will now preload the application by default (disable with `preload_app! false`). We believe this is a better default, but may cause issues in non-Rails applications if you do not have the proper `before` and `after` fork hooks configured. See documentation for your framework. Rails users do not need to change anything. **Please note that it is not possible to use [the phased restart](docs/restart.md) with preloading.**
 * tcp mode and daemonization have been removed without replacement. For daemonization, please use a modern process management solution, such as systemd or monit.
 * `connected_port` was renamed to `connected_ports` and now returns an Array, not an Integer.
 

README.md

@@ -146,7 +146,7 @@ before_fork do
 end
 ```
 
-Preloading can’t be used with phased restart, since phased restart kills and restarts workers one-by-one, and preload_app copies the code of master into the workers.
+Preloading can’t be used with phased restart, since phased restart kills and restarts workers one-by-one, and `preload_app!` copies the code of master into the workers.
 
 ### Error handling