Add code of conduct to contributing guide
Add code of conduct to contributing guide

DropsOfSerenity/refills,greyhwndz/refills,tranc99/refills,greyhwndz/refills,thoughtbot/refills,mehdroid/refills,thoughtbot/refills,greyhwndz/refills,hlogmans/refills,cllns/refills,DropsOfSerenity/refills,dydx/refills,tranc99/refills,smithdamen/refills,thoughtbot/refills,mehdroid/refills,mehdroid/refills,DropsOfSerenity/refills,dydx/refills,thoughtbot/refills,dydx/refills,smithdamen/refills,cllns/refills,cllns/refills,tranc99/refills,hlogmans/refills,hlogmans/refills,mehdroid/refills,greyhwndz/refills,hlogmans/refills,smithdamen/refills,dydx/refills,DropsOfSerenity/refills,cllns/refills,smithdamen/refills,tranc99/refills