docs: document the relayListen conf param
docs: document the relayListen conf param

fixes #671

alienth/bosun,alienth/bosun,simnv/bosun,seekingalpha/bosun,melifaro/bosun,csmith-palantir/bosun,leapar/bosun,simnv/bosun,bosun-monitor/bosun,bosun-monitor/bosun,augporto/bosun,seekingalpha/bosun,bookingcom/bosun,augporto/bosun,seekingalpha/bosun,csmith-palantir/bosun,leapar/bosun,leapar/bosun,mhenderson-so/bosun,leapar/bosun,alienth/bosun,augporto/bosun,bosun-monitor/bosun,alienth/bosun,GROpenSourceDev/bosun,csmith-palantir/bosun,bookingcom/bosun,bosun-monitor/bosun,GROpenSourceDev/bosun,mhenderson-so/bosun,augporto/bosun,TrentScholl/bosun,bosun-monitor/bosun,simnv/bosun,TrentScholl/bosun,bookingcom/bosun,mhenderson-so/bosun,mhenderson-so/bosun,TrentScholl/bosun,csmith-palantir/bosun,bosun-monitor/bosun,TrentScholl/bosun,leapar/bosun,alienth/bosun,TrentScholl/bosun,melifaro/bosun,melifaro/bosun,GROpenSourceDev/bosun,simnv/bosun,melifaro/bosun,melifaro/bosun,mhenderson-so/bosun,GROpenSourceDev/bosun,bookingcom/bosun,seekingalpha/bosun,alienth/bosun,csmith-palantir/bosun,simnv/bosun,bookingcom/bosun,seekingalpha/bosun,GROpenSourceDev/bosun,mhenderson-so/bosun,augporto/bosun,melifaro/bosun,TrentScholl/bosun,seekingalpha/bosun,leapar/bosun,simnv/bosun,csmith-palantir/bosun,bookingcom/bosun,augporto/bosun,GROpenSourceDev/bosun