Add note about 80 columns max to CONTRIBUTING file
Add note about 80 columns max to CONTRIBUTING file

LineMetrics/cowboy,lpgauth/cowboy,manastech/cowboy,venkateshreddy/cowboy,rabbitmq/cowboy,heroku/cowboy,heroku/cowboy,acrispin/cowboy,K2InformaticsGmbH/cowboy,sile/cowboy,dangjun625/cowboy,linearregression/cowboyku,odo/cowboy,paulperegud/cowboy,yangchengjian/cowboy,manastech/cowboy,layerhq/cowboy,unisontech/cowboy,noname007/cowboy,layerhq/cowboy,binarin/cowboy,essen/cowboy,piboye/cowboy,cad627/cowboy,LineMetrics/cowboy,lpgauth/cowboy,kivra/cowboy,LineMetrics/cowboy,callsign-core/cowboy_hybi00,MSch/cowboy,heroku/cowboyku,bsmr-erlang/cowboy,Reimerei/cowboy,omusico/cowboy,unisontech/cowboy,yangchengjian/cowboy,bobos/ecweb,piboye/cowboy,callsign-core/cowboy_hybi00,CrankWheel/cowboy,276361270/cowboy,cad627/cowboy,hairyhum/cowboy,grahamrhay/cowboy,nviennot/cowboy,binarin/cowboy,ninenines/cowboy,rbalint/pkg-erlang-cowboy,ferd/cowboyku,pap/cowboy,essen/cowboy,turtleDeng/cowboy,imdeps/cowboy