Add basic README getting started

[philips]

Lots of people want to play with this and are pinging @polvi's monokube repo: polvi/monokube#2

People just need a quick getting started. We can mostly just port stuff from https://github.com/polvi/monokube#monokube

[philips]

@derekparker do you think you could take a swing at this?

[derekparker]

@philips absolutely.

[aaronlevy]

fixed in: #16

Also, we do have some quick-hack instructions in:
https://github.com/coreos/bootkube/tree/master/hack/single-node
https://github.com/coreos/bootkube/tree/master/hack/multi-node