Clarify username in API authentication docs
Clarify username in API authentication docs

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