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This is totally hackish anyway but maybe this variant will look a bit
better.

- Everybody doing a manual upgrade will go through the download page
  while they might not all go through /doc/upgrade.
- Reading the release notes while downloading sounds less trouble.
- People doing automatic upgrades are already pointed to the release
  notes.

If we want more people to read the release notes, the real solution will
be in #17068.

On the download page:

- 'windows linux mac' is equivalent to 'usb'
- 'upgrade-tails upgrade-windows' is equivalent to 'upgrade'

We propose manual upgrades from a regular OS because it might be:

  - Faster to do download (eg. Torrent)
  - Less intrusive
  - Possible to do proactively

Even though it might be a bit less safe.

Now that we have a procedure for each operating system and no procedure
anymore in the generic header ("Verify using OpenPGP"), I feel the need
to duplicate this step at the beginning of each procedure.

I also tested these instructions with GPG Suite 2019.1 and they still
work :)

Currently translated at 17.7% (11 of 62 strings)

Translation: Tails/wiki/src/news/version_3.14.1.*.po
Translate-URL: http://translate.tails.boum.org/projects/tails/wikisrcnewsversion_3141po/pt/

Currently translated at 39.0% (16 of 41 strings)

Translation: Tails/wiki/src/news/version_3.11.*.po
Translate-URL: http://translate.tails.boum.org/projects/tails/wikisrcnewsversion_311po/it/

It's probably less dangerous and confusing to show upgrade first to
people who want to install than to show install first to people who want
to upgrade as they could erase their persistence is their follow the
installation instructions

- Separate them more
- Clarify the impact on persistent storage
- Put on the same level as download only in release notes

This reverts commit 9932a887, reversing
changes made to a6942f92.