[Tails-l10n] [Review](fr) Translation of contribute page

Hi,

please review and merge translation of that page:

wiki/src/contribute.fr.po

commit 4d0f5cc, master branch, mercedes508 repo

Reviewer should note that the "second part" of that page is not
translated, it's on purpose because of that sentence:

"This section is only in English, because there are currently no way to
contribute to Tails if you do not understand English."

Translating everything after that warning could make users believe it's
possible because it's translated anyway. But unfortunately it's not.

Cheers.