io: add example for Pipe

Change-Id: I24374accf48d43edf4bf27ea6ba2245ddca558ad
Reviewed-on: https://go-review.googlesource.com/50910
Reviewed-by: Giovanni Bajo <rasky@develer.com>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/io/example_test.go

@@ -243,3 +243,19 @@ func ExampleMultiWriter() {
 	// some io.Reader stream to be read
 	// some io.Reader stream to be read
 }
+
+func ExamplePipe() {
+	r, w := io.Pipe()
+
+	go func() {
+		fmt.Fprint(w, "some text to be read\n")
+		w.Close()
+	}()
+
+	buf := new(bytes.Buffer)
+	buf.ReadFrom(r)
+	fmt.Print(buf.String())
+
+	// Output:
+	// some text to be read
+}