Use example for i19 update

I expected i19 update to work using the rails config.

When the default locale was missing I tried to debug the @default_locale code looking for a bug, later I read the  " Add a `i19.config.yml` file so it is not necessary to write all the parameters on the CLI all the time" comment

It would be good to have a first example, if you just read the point 3 -> When you are done coding you go to the console and run: `bundle exec i19 update`  seems that It should work as it is