Fix link to Transifex documentation
Originally created by @matsa on #7514 (Redmine)
Transifex documentation was moved, the link is now broken,
see https://tails.boum.org/contribute/how/translate/#index1h2
Originally created by @matsa on #7514 (Redmine)
Transifex documentation was moved, the link is now broken,
see https://tails.boum.org/contribute/how/translate/#index1h2