readme: add support level badge.
readme: add support level badge.

cschindlbeck/kuka_experimental,ros-industrial/kuka_experimental,tingelst/kuka_experimental,BrettHemes/kuka_experimental,ros-industrial/kuka_experimental,tingelst/kuka_experimental,rtonnaer/kuka_experimental,rtonnaer/kuka_experimental,BrettHemes/kuka_experimental,ivareri/kuka_experimental,ivareri/kuka_experimental,cschindlbeck/kuka_experimental