fedora-upgrade says: Going to upgrade your Fedora to version 20. You may want to read Release Notes: http://docs.fedoraproject.org/release-notes/ which redirects to http://docs.fedoraproject.org/en-US/Fedora/18/html/Release_Notes/.
I'll open a ticket with Infra to get this redirect fixed.
Opps, wrong address.
https://fedorahosted.org/fedora-infrastructure/ticket/4056