Add designs to a documentation folder

[nherriot]

From notes taken it FOSDEM 2019, it seems to be clear that i need to put our design documents into a document folder in the case where people may want to try this out, but understand how the thing actually works!

1. Take sequence diagrams and place into a design folder.
2. Take architecture diagrams and place into a design folder.
3. Consider having a readme or WiKi to discuss all this and explain how the thing works.
4. Implement a WiKi anyway - it needs to have diagrams on how it works and what it looks like.