[racket] deprecating planet version using para. in planet description?

> Greg, would you be willing to write up your instructions for this as
> part of the package system documentation?

Yes.

I'm a bit rusty contributing; it's been awhile. And I'm still not
accustomed to the new source layout (e.g. I often manage to end up in
dirs with just `compiled` subdirs, then back up and find where the
source actually is, nowadays).

So although it will probably be a low signal:ratio effort (I'll
probably spend more time finding the .scrbl than editing it ;)), I'll
give it a shot. Good exercise for me, anyway.