Update documentation to use the new script

SETUP.md

@@ -91,10 +91,9 @@ $ php artisan tinker
 Using Laravel's [Mix](https://laravel.com/docs/5.5/mix).
 ```bash
 # generate translations for langjs
-$ php artisan lang:js resources/assets/js/messages.js
-# generate routes for laroute
-$ php artisan laroute:generate
-# build assets (from `docker-compose exec yarn sh` when using docker)
+# and routes for laroute
+$ bin/update_locales_and_routes_js
+# build assets (should be done automatically if using docker)
 $ yarn run development
 ```