add PrefixHostAnnouncement docstring
add PrefixHostAnnouncement docstring

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