Create a Discourse / Piazza forum? What to use?

Arvid:
"Previous years of Battlecode have had forums, which is a nice way of having organized discussions and troubleshooting. Discourse seems like a good tool for this." also he suggested Piazza to me
https://github.com/battlecode/battlecode20/issues/13

What would be good to have? (can do two or more)
Also once we figure out what we'd like, we should make it?