Add go report badge to readme file

README.md

@@ -2,6 +2,7 @@
 
 [![Build Status](https://travis-ci.org/goharbor/harbor.svg?branch=master)](https://travis-ci.org/goharbor/harbor)
 [![Coverage Status](https://coveralls.io/repos/github/goharbor/harbor/badge.svg?branch=master)](https://coveralls.io/github/goharbor/harbor?branch=master)
+[![Go Report Card](https://goreportcard.com/badge/github.com/goharbor/harbor)](https://goreportcard.com/report/github.com/goharbor/harbor)
 
 **Note**: The `master` branch may be in an *unstable or even broken state* during development.
 Please use [releases](https://github.com/vmware/harbor/releases) instead of the `master` branch in order to get stable binaries.