[Tails-l10n] Updates on the documentation for translations w…

Dear translators,

I updated the documentation for translations with git and would be glad
to have your feedback.

The updated version is here:
https://git-tails.immerda.ch/elouann/tails/tree/wiki/src/contribute/how/translate/with_Git.mdwn?h=doc/10076-fix-translating-with-git

and the ticket there:
https://labs.riseup.net/code/issues/10076

Thank you,
~ elouann