Update the list of the unimplemented Docker features (and implement them)

The list of the unimplemented Docker features is outdated: https://github.com/containerd/nerdctl/blob/21590cd689246dd8ec4b3b59b843e6f04b9317e9/docs/command-reference.md?plain=1#L414-L418

• Make RO mounts RRO by default https://github.com/containerd/nerdctl/issues/2651
  • Docker-side PR: https://github.com/moby/moby/pull/45278 https://github.com/moby/moby/pull/46037
• --mount type=image https://github.com/containerd/nerdctl/pull/4993
  • Docker-side PR: https://github.com/moby/moby/pull/48798
• --security-opt writable-cgroups
  • Docker-side PR: https://github.com/moby/moby/pull/48828
• buildx debugger
• CDI https://github.com/containerd/nerdctl/pull/4170
• mount :z and :Z https://github.com/containerd/nerdctl/issues/371 https://github.com/containerd/nerdctl/pull/4639
• userns-remap mode https://github.com/containerd/nerdctl/pull/3941
• (And more, see Sub-issues below)