docs(README): add some more background
docs(README): add some more background

madharjan/discovery.etcd.io,jjamor/coreos-private-discovery-service-src,tschuy/discovery.etcd.io,coreos/discovery.etcd.io,coreos/discovery.etcd.io,jjamor/coreos-private-discovery-service-src,madharjan/discovery.etcd.io,tschuy/discovery.etcd.io