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

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

Original created by @sajolida on 15416 (Redmine)

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