cmcguinness: added main.go for gophercon 2017 contrib tutorial

Change-Id: I237fb6efce29e70019c6e92b1f7e8d37ec9c6607
Reviewed-on: https://go-review.googlesource.com/48756
Reviewed-by: Bryan Mills <bcmills@google.com>

cmcguinness/main.go

@@ -0,0 +1,17 @@
+// 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.
+
+// The cmcguinness tool displays a random number.
+package main
+
+import "fmt"
+
+// randomNumber implementation sourced from https://xkcd.com/221/.
+// chosen by a fair dice roll.
+// guaranteed to be random
+const randomNumber = 4
+
+func main() {
+	fmt.Printf("Your random number of the day is: %v", randomNumber)
+}