Proposal for Documentation Site approach

[EricZinda]

Here's a start at describing the general approach to The Documentation and distinguishing it from the wiki. It is high level and meant to give us a direction and common understanding about the "architecture" of the documentation site, including how it is built and hosted.

Once we agree on this we can start figuring out things like: what is in the docs, what format, what's the workflow etc.

Please comment @delph-in/erdw!

https://github.com/delph-in/docs/wiki/ERDW_StructureForNewDocsSite