Use old subdomain for documentation

[jessealama]

No description provided.

[spdegabrielle]

I'd prefer the information at http://old.barzilay.org/Swindle/ be migrated to https://github.com/racket/swindle/blob/master/swindle.scrbl rather than depending on the archive website.

I made a call to action post at https://racket.discourse.group/t/swindle-clos-for-racket/ and https://www.reddit.com/r/Racket/comments/ygh8do/swindleclos_on_racket_call_to_action/?utm_source=share&utm_medium=web2x&context=3

[elibarzilay]

FWIW, it would be much better to port any needed information to the documentation instead; it's certainly what I would have if it existed at the time.

(And re the discord post --- I think that much more than just documentation is needed here, the first thing is to make it actually useful with the many new things that were added to Racket since then... But the default mutation thing of CLOS makes it harder, which is kind of why I drifted away from it...)