[WIP] Add Distributed module documentation

[ktoso]

This is a very early version of Distributed module documentation; It is not polished up, may have stray sentences and sections etc.

We'll figure out how to best present the information through the pitch posted on the forums over here:

I'll also work on improving tone and voice still, right now it is not the most consistent.

For now, we can discuss what needs to be explained in this documentation and I started a forums thread for this purpose: TSPL Pitch: Distributed.