website/docproj: Correct link to wiki article

A new ideas list page was added by dbaio@ on 2021-06-17, so to ensure
that people get sent to the correct place, update the link in the
documentation.

I've also setup a redirect on the wiki, to catch extranenous links from
places outside of project control.

PR: 260179
Reported by: PauAmma, parv (on IRC) <parv.0zero9+freebsd@gmail.com>