Minor improvements to the REST principles chapter

Well written summary!
While reading through, I made some clarifications (from my POV).

In addendum, see [a post of mine clarifying REST concepts](http://hyperrest.github.io/2013-03-30-rest-api-concepts/#content). To a great extent, I think it still is a good analogy (1.5y after).
I intended to move away from "store that information". As a separation of concerns, the REST *server* is in charge of the content (what, how, when) and how pieces of that content is best linked together (not just links, but views too). The initial phrasing sounds very much like "it's stored in Riak, uses a message queue, decides when to use binary payloads" etc i.e. misleading use of `efficiently`