doc: replace gitter logo with discord

Author: elevatebart

README.md

@@ -3,6 +3,10 @@
 [![npm](https://img.shields.io/npm/v/vue-docgen-api.svg)](https://www.npmjs.com/package/vue-docgen-api)
 [![Build Status](https://travis-ci.org/vue-styleguidist/vue-docgen-api.svg?branch=master)](https://travis-ci.org/vue-styleguidist/vue-docgen-api)
 [![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg)](https://github.com/semantic-release/semantic-release)
+<a href="https://discordapp.com/channels/325477692906536972/538786416092512278">
+  <img src="https://img.shields.io/discord/325477692906536972.svg?logo=discord"
+alt="chat on Discord">
+</a>
 
 `vue-docgen-api` is a toolbox to help extracting information from [Vue](https://vuejs.org/) components, and generate documentation from it.