Add CCI badge for containerd
Closes
[![Build Status](https://travis-ci.org/containerd/containerd.svg?branch=master)](https://travis-ci.org/containerd/containerd)
[![FOSSA Status](https://app.fossa.io/api/projects/git%2Bhttps%3A%2F%2Fgithub.com%2Fcontainerd%2Fcontainerd.svg?type=shield)](https://app.fossa.io/projects/git%2Bhttps%3A%2F%2Fgithub.com%2Fcontainerd%2Fcontainerd?ref=badge_shield)
[![Go Report Card](https://goreportcard.com/badge/github.com/containerd/containerd)](https://goreportcard.com/report/github.com/containerd/containerd)
+[![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/1271/badge)](https://bestpractices.coreinfrastructure.org/projects/1271)
containerd is an industry-standard container runtime with an emphasis on simplicity, robustness and portability. It is available as a daemon for Linux and Windows, which can manage the complete container lifecycle of its host system: image transfer and storage, container execution and supervision, low-level storage and network attachments, etc.
