Bitcoin Design Guide Jam Session #20: Lightning wrap-up encore

Just like in our last jam session, we talked about wrapping up Lightning and what's next. Déjà vu? Almost. We did wrap up a several more pages since, and we also built on discussions from last time. Our next community call is in 9 days, we should be able to wrap up and make a big announcement that day (including Twitter, newsletter & call).

https://github.com/BitcoinDesign/Meta/issues/217