Add goreportcard.com bagde

Author: leonelquinteros

README.md

@@ -1,5 +1,6 @@
 [![GoDoc](https://godoc.org/github.com/leonelquinteros/gotext?status.svg)](https://godoc.org/github.com/leonelquinteros/gotext)
 [![Build Status](https://travis-ci.org/leonelquinteros/gotext.svg?branch=master)](https://travis-ci.org/leonelquinteros/gotext)
+[![Go Report Card](https://goreportcard.com/badge/github.com/leonelquinteros/gotext)](https://goreportcard.com/report/github.com/leonelquinteros/gotext)
 
 # Gotext