[Tails-l10n] [doc][fr] Merge Request

Hi,

I'd like you (empowered people) to please merge master branch of
mercedes508 repo, from this state:

commit 4996ecd

It does include several reviews:

wiki/src/download.fr.po
wiki/src/support/known_issues.fr.po
wiki/src/doc/first_steps/usb_installation.fr.po
wiki/src/doc/get/trusting_tails_signing_key.fr.po
wiki/src/doc/first_steps/usb_reset.fr.po
wiki/src/doc/first_steps/usb_reset.intro.fr.po
wiki/src/doc/first_steps/usb_reset/linux.fr.po
wiki/src/doc/first_steps/usb_reset/windows.fr.po
wiki/src/doc/encryption_and_privacy/secure_deletion.fr.po

and minor changes in :

wiki/src/doc/encryption_and_privacy/truecrypt.fr.po

Thanks