Point to Git introductory doc from various new contributors doc
Originally created by @intrigeri on #6426 (Redmine)
#6336 (closed) links to great Git newbie doc from the translators documentation.
We should first factorize this piece of doc in another place (e.g. some subsection of contribute/git’s “General information”, or contribute/git/learn), and then link to there from contribute/how/{documentation,translate,website}.
Edited by intrigeri