Listens for a specific directory and emits a log message when an update occurs into this one, like as file modification, addition or removal.
ruby bin/watcher start
While this has been running, a Listener(https://rubygems.org/gems/listen) will be, of course, listen to a specific directory
What about that directory? This it's included into a YAML file - config/config.yml - as value of folder key.