docs(README): add codecov badge

Author: kkweon

README.md

@@ -1,6 +1,7 @@
 # paperswithcode-go
 [![Go](https://github.com/codingpot/paperswithcode-go/actions/workflows/go.yaml/badge.svg)](https://github.com/codingpot/paperswithcode-go/actions/workflows/go.yaml)
 [![Go Reference](https://pkg.go.dev/badge/github.com/codingpot/paperswithcode-go.svg)](https://pkg.go.dev/github.com/codingpot/paperswithcode-go)
+[![codecov](https://codecov.io/gh/codingpot/paperswithcode-go/branch/main/graph/badge.svg?token=MhzDKZOtWK)](https://codecov.io/gh/codingpot/paperswithcode-go)
 
 client code repository for paperswithcode's official APIs