add first pass of proposal to README

@shiffman Would love feedback!  Also, let me know if I should [propose](https://docs.google.com/a/nyu.edu/forms/d/1sdvsw7zjgOTc3y79ID3p-JaBaO2wxHy5t8q6XWXfDvE/viewform) it right away, or wait until the plan is "finalized", or if I shouldn't bother.  Thanks!