Add a link to a tutorial.

30.about/10.contributing/page.en.md

@@ -71,6 +71,8 @@ You can use your favorite text editor.
 
 Here are some [Git GUI clients](https://git-scm.com/downloads/guis), if the CLI feels too hard.
 
+Here is a nice tutorial (in french) : https://openclassrooms.com/fr/courses/1233741-gerez-vos-codes-source-avec-git
+
 > Note that during the alpha we're using port `10022` for ssh.