README.md in annoy-rb-0.1.0 vs README.md in annoy-rb-0.2.0

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 # Annoy.rb
 
 [![Build Status](https://travis-ci.org/yoshoku/annoy.rb.svg?branch=master)](https://travis-ci.org/yoshoku/annoy.rb)
 [![Gem Version](https://badge.fury.io/rb/annoy-rb.svg)](https://badge.fury.io/rb/annoy-rb)
 [![License](https://img.shields.io/badge/License-Apache%202.0-yellowgreen.svg)](https://github.com/yoshoku/annoy.rb/blob/master/LICENSE.txt)
+[![Documentation](http://img.shields.io/badge/api-reference-blue.svg)](https://yoshoku.github.io/annoy.rb/doc/)
 
 Annoy.rb is a Ruby binding for the [Annoy (Approximate Nearest Neighbors Oh Yeah)](https://github.com/spotify/annoy).
 
 ## Installation
 