Merge pull request containerd#59 from gliptak/patch-1

Add GoReportCard badge to README

README.md

@@ -3,6 +3,7 @@
 [![Build Status](https://travis-ci.org/containerd/cgroups.svg?branch=master)](https://travis-ci.org/containerd/cgroups)
 [![codecov](https://codecov.io/gh/containerd/cgroups/branch/master/graph/badge.svg)](https://codecov.io/gh/containerd/cgroups)
 [![GoDoc](https://godoc.org/github.com/containerd/cgroups?status.svg)](https://godoc.org/github.com/containerd/cgroups)
+[![Go Report Card](https://goreportcard.com/badge/github.com/containerd/cgroups)](https://goreportcard.com/report/github.com/containerd/cgroups)
 
 Go package for creating, managing, inspecting, and destroying cgroups.
 The resources format for settings on the cgroup uses the OCI runtime-spec found