contrib: add reference to LinuxKit project
contrib: add reference to LinuxKit project

Just a simple README with a pointer to the project.

Signed-off-by: Ian Campbell <a8db091655a7f47ecb9c39a2d278e9662e440dc0@docker.com>

thaJeztah/containerd,zhangzhenhao/cri-containerd,w9n/cri-containerd,zhangzhenhao/cri-containerd,mikebrow/cri-containerd,dmcgowan/containerd,mikebrow/containerd,zhangzhenhao/cri-containerd,dmcgowan/containerd,mikebrow/cri-containerd,mikebrow/containerd,vdemeester/containerd,containerd/containerd,estesp/containerd,estesp/containerd,vdemeester/containerd,thaJeztah/containerd,containerd/containerd,w9n/cri-containerd,mikebrow/cri-containerd,w9n/cri-containerd