Add shiny open graph information

[hoergen]

When you actually send the link of the directory with the public servers to people and the software is extracting the open graph information, this looks kind of ugly right now.

This is, what you get, if you use https://dir.friendica.social/servers

Maybe we should discuss in our forums (Friendica Support?) what we want to show on that page. In my opinion there should be at least a picture, maybe with our new mascot? Or something like "join friendica" .