Improve the MR guidelines from the CONTRIBUTING guide
Improve the MR guidelines from the CONTRIBUTING guide

[ci skip]

Signed-off-by: Rémy Coutable <4ea0184b9df19e0786dd00b28e6daa4d26baeb3e@rymai.me>

darkrasid/gitlabhq,jirutka/gitlabhq,t-zuehlsdorff/gitlabhq,jirutka/gitlabhq,htve/GitlabForChinese,t-zuehlsdorff/gitlabhq,dreampet/gitlab,jirutka/gitlabhq,dplarson/gitlabhq,t-zuehlsdorff/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,jirutka/gitlabhq,htve/GitlabForChinese,stoplightio/gitlabhq,mmkassem/gitlabhq,dplarson/gitlabhq,dplarson/gitlabhq,mmkassem/gitlabhq,htve/GitlabForChinese,iiet/iiet-git,axilleas/gitlabhq,stoplightio/gitlabhq,dplarson/gitlabhq,axilleas/gitlabhq,t-zuehlsdorff/gitlabhq,dreampet/gitlab,htve/GitlabForChinese,stoplightio/gitlabhq,axilleas/gitlabhq,darkrasid/gitlabhq,dreampet/gitlab,iiet/iiet-git,iiet/iiet-git,iiet/iiet-git,darkrasid/gitlabhq,axilleas/gitlabhq,darkrasid/gitlabhq,mmkassem/gitlabhq