[Tails-l10n] [fr](review) upgrade pages

Hello, I update some pages about upgrade.

At the same time, I fix a missing space in the english version.

I don't update an inline in first_steps/upgrade.fr.po, I have an error
with this. I think you should review without change that.

Repo : https://git-tails.immerda.ch/xin/tails/
Branch : translate/upgrade
Last Commit : a1f3729c31d49ccad8960640685bb95acf1ea2f0

Cheers.
xin