Add release notes for containerd 1.2.0
Add release notes for containerd 1.2.0

Prepare release notes ahead of 1.2.0-rc.1

Signed-off-by: Derek McGowan <e1c79a582b6629e6b39e9679f4bb964d25db4aa8@mcgstyle.net>

thaJeztah/containerd,thaJeztah/containerd,vdemeester/containerd,dmcgowan/containerd,vdemeester/containerd,miaoyq/containerd,mikebrow/containerd,containerd/containerd,estesp/containerd,mikebrow/containerd,crosbymichael/containerd,estesp/containerd,containerd/containerd,dmcgowan/containerd,miaoyq/containerd,crosbymichael/containerd