Add `docker pulls` badge as we passed 2M pulls (#1345)
Add `docker pulls` badge as we passed 2M pulls (#1345)

We passed 2M docker pulls from DockerHub. Adds `docker pulls` badge
to README.md

Signed-off-by: Yong Tang <765086fe2e0c1f980161f127fec596800f327f62@outlook.com>
chrisohaver/coredns,jremond/coredns,johnbelamaric/coredns,miekg/coredns,johnbelamaric/coredns,ii/coredns,ii/coredns,miekg/coredns,jremond/coredns,coredns/coredns,yongtang/coredns