message: Add a readme badge about discord
diff: <a href="https://github.com/ethereum-ts/TypeChain/actions"><img alt="Build Status" src="https://github.com/ethereum-ts/TypeChain/workflows/CI/badge.svg"></a>
  <img alt="Downloads" src="https://img.shields.io/npm/dm/typechain.svg">
  <a href="/package.json"><img alt="Software License" src="https://img.shields.io/badge/license-MIT-brightgreen.svg?style=flat-square"></a>
  + <a href="https://discord.gg/cpbj5BDq"><img alt="Join our discord!" src="https://img.shields.io/discord/895381864922091630.svg?color=7289da&label=deth&logo=discord&style=flat-square"></a>
  </p>
  <p align="center">
  