add note that a namespace cannot be named "version"
add note that a namespace cannot be named "version"

Signed-off-by: Iceber Gu <78ca334faffe22661af7aca8231f7bac3769751c@daocloud.io>

thaJeztah/containerd,containerd/containerd,estesp/containerd,mikebrow/containerd,estesp/containerd,thaJeztah/containerd,containerd/containerd,mikebrow/containerd