examples: add most docstrings

examples/add/asm.go

@@ -8,6 +8,7 @@ import (
 
 func main() {
 	TEXT("Add", "func(x, y uint64) uint64")
+	Doc("Add adds x and y.")
 	x := Load(Param("x"), GP64v())
 	y := Load(Param("y"), GP64v())
 	ADDQ(x, y)

examples/add/stub.go

@@ -2,4 +2,5 @@
 
 package add
 
+// Add adds x and y.
 func Add(x uint64, y uint64) uint64