New Mastodon recipe (swarm)

New recipe - Mastodon, like Twitter on the Fediverse. Check out the Docker Swarm recipe!

Mastodon is an open-source, federated (i.e., decentralized) social network, inspired by Twitter's "microblogging" format, and used by upwards of 6.4M early-adopters, to share links, pictures, video and text.