Don't load Rails for most tasks; improve docs
Don't load Rails for most tasks; improve docs

We don't need Rails for any tasks except the detailed guidance
registration.

While I'm in here, add `desc` values for each task so they actually turn
up when running `rake -T`.

robinwhittleton/whitehall,askl56/whitehall,alphagov/whitehall,hotvulcan/whitehall,YOTOV-LIMITED/whitehall,askl56/whitehall,hotvulcan/whitehall,ggoral/whitehall,YOTOV-LIMITED/whitehall,alphagov/whitehall,ggoral/whitehall,askl56/whitehall,hotvulcan/whitehall,robinwhittleton/whitehall,askl56/whitehall,alphagov/whitehall,ggoral/whitehall,robinwhittleton/whitehall,YOTOV-LIMITED/whitehall,alphagov/whitehall,robinwhittleton/whitehall,hotvulcan/whitehall,YOTOV-LIMITED/whitehall,ggoral/whitehall