[Tails-l10n] [fr](review) 3.0, first branch

Hello, I made a branch with few things to start 3.0 translation.

I change:
doc/about/features
doc/about/requirements
doc/first_steps/persistence/upgrade
doc/advanced_topics/virtualization/virtualbox

Repo: https://git-tails.immerda.ch/xin/tails/
Branch: translate/3.0/first
Last Commit: 9296c27b8a53802ca080c967305b9204e66ef4d6

To review, you can use this commands:
git checkout origin/testing
git checkout -b name_of_your_review_branch
git merge xin/translate/3.0/first

Cheers.
xin