Merge pull request #1 from heppu/cov-bagde

Add codecov badge

Author: heppu

README.md

@@ -1,5 +1,5 @@
 # errgroup
 
-[![Go Reference](https://pkg.go.dev/badge/github.com/heppu/errgroup.svg)](https://pkg.go.dev/github.com/heppu/errgroup)
+[![Go Reference](https://pkg.go.dev/badge/github.com/heppu/errgroup.svg)](https://pkg.go.dev/github.com/heppu/errgroup) [![codecov](https://codecov.io/github/heppu/errgroup/graph/badge.svg?token=H3u7Ui9PfC)](https://codecov.io/github/heppu/errgroup)
 
 Golang waitgroup with error handling