Update README.md

README.md

@@ -1,6 +1,7 @@
 # go-future
 
 [![codecov](https://codecov.io/github/jizhuozhi/go-future/graph/badge.svg?token=9UZDVRZCQM)](https://codecov.io/github/jizhuozhi/go-future)
+[![goreport](https://goreportcard.com/badge/github.com/jizhuozhi/go-future)](https://goreportcard.com/badge/github.com/jizhuozhi/go-future)
 
 The `Promise` provides a facility to store a value or an error that is later acquired asynchronously via a `Future` created by the `Promise` object. Note that the `Promise` object is meant to be used only once.