Document how to manually upgrade to 3.6 and 3.6.1 for non-English users

Originally created by @sajolida on #15416 (Redmine)

• Tails 3.5 is broken in non-English languages.
• Automatic upgrades to 3.6 are broken.

The combination completely breaks upgrade for non-English users.

Feature Branch: doc/15416-manual-upgrade-from-3.5

Related issues

• Related to #15233 (closed)
• Related to #15427 (closed)