fix upgrade notification
Originally created by Tails on #5579 (Redmine)
When a new version is out, users receive a notification message.
This message should point in some way to usb upgrade instructions.
It does "point in some way": the notification message points to the security announce, that reads "We strongly urge you to upgrade to Tails 0.17.2; (pointing to the release announce), that itself has a "I want to try it / to upgrade!" section. That section points to "Getting started", which is overkill for long-time users, so there’s room for improvement here. However, I’m not sure I want us to point users to upgrade instructions without giving them a chance to read the release notes including known issues, so IMHO the problem does not lie in the upgrade notification.
Calling this a potential documentation issue, then.
Feature Branch: doc/fix-upgrade-notification