improve documentation for storagemanager.go
improve documentation for storagemanager.go

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