Add link to prior work on promise-as-monad

Just watched the talk, really enjoyed it, thank you very much. I was
waiting for you to get to the promise-as-monad punchline the whole
time, which was great, but then when you sort of took credit for the
idea I had to regoogle some of the things I had been reading about
the concept--sometime over a year ago. Check out the great post at
the URL I added. To your credit, though, these are great concepts
that deserve wider consideration, and thanks again for speaking on
them.