Noob question. If Nostr relays are what store user notes, can this scale yo millions and eventually billions of people? The relays would eventually have to become massive? Bitcoin has an incentive for the miners in the form of block subsidy and transaction fees. What's the incentive to run a relay other than helping create a decentralized platform? My question is..is this sustainable in the future and can this scale up to support millions of Nostriches?