os/exec: add example for Cmd.Run

Change-Id: Ic47198bc8bf5baabfcf4d0599825eab30d7b126c
Reviewed-on: https://go-review.googlesource.com/48853Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/exec/example_test.go

@@ -57,6 +57,13 @@ func ExampleCmd_Output() {
 	fmt.Printf("The date is %s\n", out)
 }
 
+func ExampleCmd_Run() {
+	cmd := exec.Command("sleep", "1")
+	log.Printf("Running command and waiting for it to finish...")
+	err := cmd.Run()
+	log.Printf("Command finished with error: %v", err)
+}
+
 func ExampleCmd_Start() {
 	cmd := exec.Command("sleep", "5")
 	err := cmd.Start()