Update readme.md

add discord.

readme.md

@@ -9,6 +9,7 @@ English | [简体中文](readme-cn.md)
 [![Go Report Card](https://goreportcard.com/badge/github.com/zeromicro/go-zero)](https://goreportcard.com/report/github.com/zeromicro/go-zero)
 [![Release](https://img.shields.io/github/v/release/zeromicro/go-zero.svg?style=flat-square)](https://github.com/zeromicro/go-zero)
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
+[![Discord](https://img.shields.io/discord/794530774463414292?label=chat&logo=discord)](https://discord.gg/4JQvC5A4Fe)
 
 **Note: To meet the requirements of Open Source Foundation, we moved go-zero from tal-tech to zeromicro (a neutral GitHub organization).**