add documentation for control flow and error conventions
add documentation for control flow and error conventions

ChrisSchinnerl/Sia,cyrozap/Sia,ChrisSchinnerl/Sia,mtlynch/Sia,MrStrong/Sia,mharkus/Sia,kustomzone/Sia,mtlynch/Sia,NebulousLabs/Sia,NebulousLabs/Sia,mharkus/Sia,johnathanhowell/Sia,Mingling94/Sia,rivine/rivine,MrStrong/Sia,ericflo/Sia,ericflo/Sia,rivine/rivine,mnsl/Sia,mnsl/Sia