[Tails-l10n] Please review documentation improvements

Hello,

i have tried to add what has been said on the l10n-mailinglist to the
documentation for translators in order to improve the information on h
how to set up a git repo for translation work.

Please review and comment, thanks!
u.


in branch doc // 451f

wiki/src/contribute/how/translate.mdwn

[doc 724e75e] Adding detailed git documentation for translators
[doc 7ee0bbd] beauty operation on a sentence