[10.x] Update Horizon Documentation to reflect the allowed waits config values

[robinnydahl]

After investigation into why our Horizon installs are still reporting long waits after 60 seconds when it's explicitly stated otherwise in the config, we did some further research.

We have seen that the waits array in the Horizon config does not accept multiple queues passed with commas, as seen in the code itself (see link below).

https://github.com/laravel/horizon/blob/fd5c8957e08419455cce6efdfc8f2c38a812debd/src/Listeners/MonitorWaitTimes.php#L56

Due to this, the documentation seem to be outdated/incorrect and has been updated to reflect both the default wait, which is 60 seconds, and how it would look if you have multiple queues with different wait times to report on.