Update Developer Guide to explain our CQRS approach

[mgmccarthy]

@tonysurma please assign to me

[chinwobble]

@mgmccarthy hi I was wondering if you had a chance to work on this. I was keen to see what you came up with.

[mgmccarthy]

@chinwobble, too busy doing code reviews/writing code for v1 release to get to this yet, bit I do know what iwant to write.