Add a inc/ file with a link to the release notes

Originally created by @sajolida on #7665 (Redmine)

According to #7650 (closed), we need to add a link to the latest release notes in
the upgrade instructions. Let’s do this with the same trick that we do
the ISO image URL, torrent URL, and SHA256 checksum, which is using a
dedicated file in wiki/src/inc. Then we need to upgrade the release
process documentation to have this updated by the release manager.

Marking this as a task for 1.1.1, so that the RM doesn’t have to upgrade
the content of bbbfd42 manually.

This is an easy task but I’ll do it if nobody takes it over.

Feature Branch: web/7665-add-inc-file-for-release-notes