add codecov badge

readme.md

@@ -1,6 +1,7 @@
 # go-zero项目介绍
 
-![Go](https://github.com/tal-tech/go-zero/workflows/Go/badge.svg?branch=master)
+[![Go](https://github.com/tal-tech/go-zero/workflows/Go/badge.svg?branch=master)](https://github.com/tal-tech/go-zero/actions)
+[![codecov](https://codecov.io/gh/tal-tech/go-zero/branch/master/graph/badge.svg)](https://codecov.io/gh/tal-tech/go-zero)
 
 ## 1. go-zero框架背景