添加06.2.md和相关的例子与问题解答

eBook/examples/chapter_6/side_effect.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+    "fmt"
+)
+
+// this function changes reply:
+func Multiply(a, b int, reply *int) {
+    *reply = a * b
+}
+
+func main() {
+    n := 0
+    reply := &n
+    Multiply(10, 5, reply)
+    fmt.Println("Multiply:", *reply) // Multiply: 50
+}