Update design doc a bit.
Update design doc a bit.

vaibhav345/lenskit,kluver/lenskit,tajinder-txstate/lenskit,martinlaz/lenskit,amaliujia/lenskit,chrysalag/lenskit,vijayvani/Lenskit,martinlaz/lenskit,blankazucenalg/lenskit,tajinder-txstate/lenskit,kluver/lenskit,aglne/lenskit,linjunleo/lenskit,linjunleo/lenskit,binweiwu/lenskit,aglne/lenskit,blankazucenalg/lenskit,vaibhav345/lenskit,kluver/lenskit,tajinder-txstate/lenskit,kluver/lenskit,amaliujia/lenskit,kluver/lenskit,vaibhav345/lenskit,binweiwu/lenskit,tajinder-txstate/lenskit,chrysalag/lenskit,vijayvani/Lenskit,vaibhav345/lenskit