added example

example_test.go

@@ -0,0 +1,26 @@
+package dns
+
+import (
+	"fmt"
+)
+
+// Retrieve the MX records for miek.nl.
+func ExampleRR_MX() {
+	config, _ := ClientConfigFromFile("/etc/resolv.conf")
+	c := new(Client)
+	m := new(Msg)
+	m.SetQuestion("miek.nl.", TypeMX)
+	m.RecursionDesired = true
+	r, err := c.Exchange(m, config.Servers[0]+":"+config.Port)
+	if err != nil {
+		return
+	}
+	if r.Rcode != RcodeSuccess {
+		return
+	}
+	for _, a := range r.Answer {
+		if mx, ok := a.(*RR_MX); ok {
+			fmt.Printf("%s\n", mx.String())
+		}
+	}
+}