fmt: add example Sscanf

Updates golang/go#27554.

Change-Id: I2bf3d57ebeeb5dd50beffbc643a4ad10287b2c1e
GitHub-Last-Rev: 4ffae55b4b2ca9d9b2a5b2b6dcef14ce43d83544
GitHub-Pull-Request: golang/go#27954
Reviewed-on: https://go-review.googlesource.com/c/138837Reviewed-by: Rob Pike <r@golang.org>
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/fmt/example_test.go

@@ -63,6 +63,19 @@ func ExampleFscanln() {
 	// 3: ken, 271828, 3.141590
 }
 
+func ExampleSscanf() {
+	var name string
+	var age int
+	n, err := fmt.Sscanf("Kim is 22 years old", "%s is %d years old", &name, &age)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("%d: %s, %d\n", n, name, age)
+
+	// Output:
+	// 2: Kim, 22
+}
+
 func ExamplePrint() {
 	const name, age = "Kim", 22
 	fmt.Print(name, " is ", age, " years old.\n")