Add a section in the README instructing how to import with Sbt/Maven/Gradle

[joshlemer]

I found the blog post about Rapture's i18n library and am really interested in trying it out but had a heck of a time trying to find where it is. I think if you just pointed out either in the blog post or in the readme which artifacts you need for different rapture libraries it would be a big help.

Cheers! 👍
Josh