Documenting container lifecycles

Initial work landed in [1], but it doesn't get into the order of the
setup process or explain how pause/resume/signalling work [2].  If we
don't figure these things out ahead of time, I expect we'll have to
figure them out in order to land compliance testing.

[1]: opencontainers/runtime-spec#231
[2]: https://github.com/opencontainers/specs/pull/231/files#r46735313

Author: wking