add user-user speedup to release notes
add user-user speedup to release notes

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