add the stewardship label to contributing.md
add the stewardship label to contributing.md

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