Update CONTRIBUTING.md
Update CONTRIBUTING.md

added Code of Conduct
mdb/incubator-trafficcontrol,alficles/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,alficles/incubator-trafficcontrol,alficles/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,mdb/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,alficles/incubator-trafficcontrol,mdb/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,mdb/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,mdb/incubator-trafficcontrol,alficles/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,mdb/incubator-trafficcontrol,mdb/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,mdb/incubator-trafficcontrol,alficles/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,mdb/incubator-trafficcontrol,alficles/incubator-trafficcontrol,alficles/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,jeffmart/incubator-trafficcontrol,serDrem/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,alficles/incubator-trafficcontrol,mdb/incubator-trafficcontrol,alficles/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol