Document containerd configuration

[lucperkins]

containerd has a TOML-based configuration system that is not yet documented. We should generate table-style docs of configurable parameters that can easily be updated by project maintainers.

[mikebrow]

FYI:

https://github.com/containerd/containerd/blob/master/docs/man/containerd-config.toml.5.md

https://github.com/containerd/cri/blob/master/docs/config.md