Add docs badge to README

I just added the badge you requested to your README: [![Inline docs](http://inch-pages.github.io/github/jnbt/java-properties.png)](https://inch-pages.github.io/github/jnbt/java-properties) (damn, you're such an overachiever :neckbeard:)

Your status page for this project is http://inch-pages.github.io/github/jnbt/java-properties/

Thank you for your support!