Add Gitter badge (#874)

Author: gitter-badger

README.md

@@ -4,7 +4,7 @@
 ![Build Status](https://img.shields.io/travis/aws/jsii?label=Travis-CI)
 ![Build Status](https://codebuild.us-east-1.amazonaws.com/badges?uuid=eyJlbmNyeXB0ZWREYXRhIjoiOThRRFVsVlRBTEhocVZOckE0bFlFWEtwNU0xUmtNUlRRclY0R2VYTGJaOXRlaVdaVnREV2lhVGtDUzQzUDRMMCtuYWpSTWo4N1FGTEV5Zm9yZ0dEb2dBPSIsIml2UGFyYW1ldGVyU3BlYyI6InFVbktYSlpDem1YN1JCeU8iLCJtYXRlcmlhbFNldFNlcmlhbCI6MX0%3D&branch=master)
 [![npm](https://img.shields.io/npm/v/jsii)](https://www.npmjs.com/package/jsii)
-[![docker](https://img.shields.io/badge/docker-jsii%2Fsuperchain-brightgreen)](https://hub.docker.com/r/jsii/superchain)
+[![docker](https://img.shields.io/badge/docker-jsii%2Fsuperchain-brightgreen)](https://hub.docker.com/r/jsii/superchain) [![Join the chat at https://gitter.im/aws/jsii](https://badges.gitter.im/aws/jsii.svg)](https://gitter.im/aws/jsii?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 ## Overview