readme: added go report card badge
@@ -6,6 +6,7 @@ Repository
[![Build Status](https://travis-ci.org/kopia/repo.svg?branch=master)](https://travis-ci.org/kopia/repo)
[![GoDoc](https://godoc.org/github.com/kopia/repo?status.svg)](https://godoc.org/github.com/kopia/repo)
[![Coverage Status](https://coveralls.io/repos/github/kopia/repo/badge.svg?branch=master)](https://coveralls.io/github/kopia/repo?branch=master)
+[![Go Report Card](https://goreportcard.com/badge/github.com/kopia/repo)](https://goreportcard.com/report/github.com/kopia/repo)
This library implements Content-Addressable Storage Repository used by [Kopia](https://github.com/kopia/kopia) to
store its snapshots.
