Documenting how the harvest mode works.

https://bugs.launchpad.net/juju-core/+bug/1342729
Yeah, I understand that the unexpected environment terminations was a large driver for breaking out safe-mode into a more comprehensive harvesting strategy. I do feel that the None option might be a sane choice for some people, and as such, it's probably important that we document the harvest modes in user-facing documentation. And if we're documenting that, we may as well describe all behaviors so that users are fully aware of what they're doing.

What do you think?