add example

examples/stackannotate/main.go

@@ -0,0 +1,22 @@
+package main
+
+func main() {
+	var n int
+	for i := 0; i < 10; i++ {
+		n += foo(1)
+	}
+	println(n)
+	<-chan struct{}(nil)
+}
+
+func foo(a int) int {
+	return bar(a, 2)
+}
+
+func bar(a int, b int) int {
+	s := 3
+	for i := 0; i < 100; i++ {
+		s += a * b
+	}
+	return s
+}