message: Add a Gitter chat badge to README.md
diff: > Documentation generator for TypeScript projects.
  -[![Build Status](https://travis-ci.org/TypeStrong/typedoc.svg?branch=master)](https://travis-ci.org/TypeStrong/typedoc) [![NPM version](https://badge.fury.io/js/typedoc.svg)](http://badge.fury.io/js/typedoc)
  -
  +[![Build Status](https://travis-ci.org/TypeStrong/typedoc.svg?branch=master)](https://travis-ci.org/TypeStrong/typedoc)
  +[![NPM Version](https://badge.fury.io/js/typedoc.svg)](http://badge.fury.io/js/typedoc)
  +[![Chat on Gitter](https://badges.gitter.im/TypeStrong/typedoc.svg)](https://gitter.im/TypeStrong/typedoc?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
  ## Installation
  