[Tails-l10n] [fr](review) custom programs

Hello, I improve the file for custom programs in the tails repository.
It's for testing branch.
Please review.

Repo: https://git-tails.immerda.ch/xin/tails/
Branch: translate/custom_programs
Last Commit: 2f3324f9a3bf307926f546e75115710067088d2e

Cheers.
xin