Specify in doc how to set config file

[sudodoki]

Didn't quite get how https://github.com/enginespot/js-beautify-sublime#settings should work & .jsbeautifyrc in project root didn't work for me.

[Lexicality]

This is the only file that settings are loaded from. (Unless #12 gets merged)

[octalmage]

Thanks, was having trouble figuring this out. It would be cool if it opened this file on install with the default settings.