Ajout des fonctionnalités de fork/merge

developpement/images/documentation_clone_gitlab.png

developpement/images/documentation_fork_gitlab1.png

developpement/images/documentation_fork_gitlab1_1.png

developpement/images/documentation_fork_gitlab2.png

developpement/images/documentation_fork_gitlab3.png

developpement/images/documentation_merge_gitlab1.png

developpement/images/documentation_merge_gitlab2.png

developpement/images/documentation_merge_gitlab3.png

developpement/images/documentation_merge_gitlab4.png

developpement/images/documentation_merge_gitlab5.png

developpement/participation_documentation.md