strings: add example for IndexByte

Change-Id: Ib6a59735381ce744553f1ac96eeb65a194c8da10
Reviewed-on: https://go-review.googlesource.com/48860Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/strings/example_test.go

@@ -119,6 +119,15 @@ func ExampleIndexAny() {
 	// -1
 }
 
+func ExampleIndexByte() {
+	fmt.Println(strings.IndexByte("golang", 'g'))
+	fmt.Println(strings.IndexByte("gophers", 'h'))
+	fmt.Println(strings.IndexByte("golang", 'x'))
+	// Output:
+	// 0
+	// 3
+	// -1
+}
 func ExampleIndexRune() {
 	fmt.Println(strings.IndexRune("chicken", 'k'))
 	fmt.Println(strings.IndexRune("chicken", 'd'))