With Feditext now accepting beta users, this adds it as the third
client to recommend so we have web and the dominant mobile platforms
covered.
This also removes the screenshots from the README, because it became a
mess trying to add a third one. Either the cells become very narrow, or
the table doubles in height. As the UI may also change over time, it
might be better to point folks at the apps instead who'll hopefully have
up to date screenshots in their storefronts.
Daenney