Add allow_failure CI documentation
Add allow_failure CI documentation

mr-dxdy/gitlabhq,allysonbarros/gitlabhq,icedwater/gitlabhq,LUMC/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,openwide-java/gitlabhq,jirutka/gitlabhq,htve/GitlabForChinese,SVArago/gitlabhq,htve/GitlabForChinese,martijnvermaat/gitlabhq,LUMC/gitlabhq,screenpages/gitlabhq,allysonbarros/gitlabhq,dplarson/gitlabhq,martijnvermaat/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,icedwater/gitlabhq,screenpages/gitlabhq,dreampet/gitlab,SVArago/gitlabhq,martijnvermaat/gitlabhq,darkrasid/gitlabhq,t-zuehlsdorff/gitlabhq,shinexiao/gitlabhq,dplarson/gitlabhq,icedwater/gitlabhq,stoplightio/gitlabhq,jirutka/gitlabhq,allysonbarros/gitlabhq,daiyu/gitlab-zh,openwide-java/gitlabhq,axilleas/gitlabhq,LUMC/gitlabhq,SVArago/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,axilleas/gitlabhq,openwide-java/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,dplarson/gitlabhq,SVArago/gitlabhq,htve/GitlabForChinese,iiet/iiet-git,axilleas/gitlabhq,iiet/iiet-git,shinexiao/gitlabhq,martijnvermaat/gitlabhq,darkrasid/gitlabhq,allysonbarros/gitlabhq,icedwater/gitlabhq,openwide-java/gitlabhq,dreampet/gitlab,iiet/iiet-git,dplarson/gitlabhq,shinexiao/gitlabhq,darkrasid/gitlabhq,mr-dxdy/gitlabhq,screenpages/gitlabhq,LUMC/gitlabhq,daiyu/gitlab-zh,dreampet/gitlab,daiyu/gitlab-zh,t-zuehlsdorff/gitlabhq,daiyu/gitlab-zh,shinexiao/gitlabhq,t-zuehlsdorff/gitlabhq,htve/GitlabForChinese,screenpages/gitlabhq,dreampet/gitlab,t-zuehlsdorff/gitlabhq,axilleas/gitlabhq,jirutka/gitlabhq,mr-dxdy/gitlabhq,darkrasid/gitlabhq,mr-dxdy/gitlabhq