Updated description to reflect improved environment handling.

I was just looking into sails environment handling and it wasn't really clear anywhere that this awesome PR has landed: https://github.com/balderdashy/sails/pull/1638
So I thought I would update this here so it would be easier to find for people.

Though one thing to note, I think it would now make more sense to not gitignore the `config/local.js` but rather `config/env/development.js` or maybe even `config/env/`. What do you think?