examples: add most docstrings

examples/stadtx/asm.go

@@ -39,6 +39,7 @@ func makelabels(name string, n int) []string {
 func main() {
 	Package("github.com/mmcloughlin/avo/examples/stadtx")
 	TEXT("Hash", "func(state *State, key []byte) uint64")
+	Doc("Hash computes the Stadtx hash.")
 
 	statePtr := Load(Param("state"), GP64v())
 	ptr := Load(Param("key").Base(), GP64v())