Added Link and Guide Description

Not a complete guide.
Group Overview Outline

Added an outline, and some content of the group overview doc.
Shared VM

Added a bit more definition. Still need to tweak it, but with the
limited information available this may be close to complete.

As more information/features are released for groups, we can add
more.
Added the Images

Oops, forgot them in the last pass.
Rewrite much of the Guide

I was very not happy with the previous version, and Andy agreed
with me. So, a rewrite must take place! This is the much improved
rewrite. :)
Merge pull request #50 from leeolayvar/groupsoverview-guide

Koding Groups