added extra notes section in release notes for installing containerd.io
added extra notes section in release notes for installing containerd.io

Signed-off-by: Andrew Hsu <f92968afc12903b4e22dfb0d2a8d9823100da266@docker.com>

londoncalling/docker.github.io,londoncalling/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,docker/docker.github.io,londoncalling/docker.github.io,londoncalling/docker.github.io,londoncalling/docker.github.io,thaJeztah/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io