Add Go report card to the badges.
# Metallb
-[![license](https://img.shields.io/github/license/google/metallb.svg?maxAge=2592000)](https://github.com/google/netboot/blob/master/LICENSE) [![Travis](https://img.shields.io/travis/google/metallb.svg?maxAge=2592000)](https://travis-ci.org/google/netboot) [![Quay.io](https://img.shields.io/badge/containers-ready-green.svg)](https://quay.io/metallb)
+[![license](https://img.shields.io/github/license/google/metallb.svg?maxAge=2592000)](https://github.com/google/netboot/blob/master/LICENSE) [![Travis](https://img.shields.io/travis/google/metallb.svg?maxAge=2592000)](https://travis-ci.org/google/netboot) [![Quay.io](https://img.shields.io/badge/containers-ready-green.svg)](https://quay.io/metallb) [![Go report card](https://goreportcard.com/badge/github.com/google/metallb)](https://goreportcard.com/report/github.com/google/metallb)
Metallb is a load-balancer implementation for bare metal Kubernetes
