rdsys needs a free software license

I'm looking through the rdsys repo, and

(a) There is no LICENSE file. I guess that means it is not yet free software, and we should fix that. We should pick a license (3-clause BSD is a good default, unless people want to argue for a different one) and put it in place.

and

(b) We should put some lines like "Copyright (c) 2021-2022, The Tor Project, Inc." in key files.