Added go report card.

Author: aren55555

README.md

@@ -1,6 +1,8 @@
 # jsonapi
 
-[![Build Status](https://travis-ci.org/google/jsonapi.svg?branch=master)](https://travis-ci.org/google/jsonapi) [![GoDoc](https://godoc.org/github.com/google/jsonapi?status.svg)](http://godoc.org/github.com/google/jsonapi)
+[![Build Status](https://travis-ci.org/google/jsonapi.svg?branch=master)](https://travis-ci.org/google/jsonapi)
+[![Go Report Card](https://goreportcard.com/badge/github.com/google/jsonapi)](https://goreportcard.com/report/github.com/google/jsonapi)
+[![GoDoc](https://godoc.org/github.com/google/jsonapi?status.svg)](http://godoc.org/github.com/google/jsonapi)
 
 A serializer/deserializer for JSON payloads that comply to the
 [JSON API - jsonapi.org](http://jsonapi.org) spec in go.