Lotus architecture document

[schomatis]

We need a high-level document outlining the architecture of the code in this repository (in general but specifically) for the audit. I can get something started and pull things together but the meat of it will need to come from the developers.

[whyrusleeping]

@schomatis if you can handle drawing up a skeleton, we can help fill it in

[schomatis]

Great, thanks.

[schomatis]

First draft completed in https://github.com/filecoin-project/lotus/tree/master/documentation/en/architecture.