NSQ roadmap post

cc @mccutchen
There's already a PR for gossip. Is WAL definitely on the roadmap? Is this doc meant to solicit feedback about whether it should be on the roadmap? Not clear from here. I think maybe some discussion of whether 0-mem-queue-size should be treated as a special case would be appropriate as well

On the flip side, I would be *super* excited about having that as a feature :)