md4: add example for New

Change-Id: I221d65fd495594ee409b999c7e0f0407b2331ac2
Reviewed-on: https://go-review.googlesource.com/49030
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

md4/md4_test/example_test.go

@@ -0,0 +1,20 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package md4_test
+
+import (
+	"fmt"
+	"io"
+
+	"golang.org/x/crypto/md4"
+)
+
+func ExampleNew() {
+	h := md4.New()
+	data := "These pretzels are making me thirsty."
+	io.WriteString(h, data)
+	fmt.Printf("%x", h.Sum(nil))
+	// Output: 48c4e365090b30a32f084c4888deceaa
+}