Fixed license initarg in architecture.builder-protocol.asd

* architecture.builder-protocol.asd
  (system architecture.builder-protocol): moved reference to COPYING
  from value of :license initarg into comment
Comment improvements in src/protocol.lisp

* src/protocol.lisp (toplevel): type fixes and slight cleanup in comment
  explaining the builder protocol
  (relate t t t null): added explanatory comment
Initial version of Tutorial section in README.org

* README.org (Tutorial): initial versions of sub-sections "Implementing
  a Consumer of Results", "Implementing a Producer of Results" and "The
  list Builder"