oci: Update docs for `oci.WithUserID`
oci: Update docs for `oci.WithUserID`

The behaviour was changed in 99df1a9e11f3 ("Set gid 0 when no group is
specified"), part of #2529.

Take the opportunity to tighten up the grammar a bit too.

Signed-off-by: Ian Campbell <9be92b3dbbd6611e3e4c9209fb3d04b4919e7cca@docker.com>

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