README/GOALS: Added section about design decisions

I realized that it would be a good idea to communicate our design decisions more clearly and even more important link to our inspiration.
OH <3<3 :)

@moonglum BTW I wanted to ping you because I have arangodb adapter for rom-rb in the roadmap. rom is now rewritten on top of a very simple adapter interface so it's ridiculously easy to add new adapters. Would love to have a chat about this project and rom. It's very likely I could add an adapter for guacamole just like I did with sequel to get sql support.