Add "download RefLens" step to documentation.
Add "download RefLens" step to documentation.

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