cmcguinness: added main.go for gophercon 2017 contrib tutorial
cmcguinness: added main.go for gophercon 2017 contrib tutorial

Change-Id: I237fb6efce29e70019c6e92b1f7e8d37ec9c6607
Reviewed-on: https://go-review.googlesource.com/48756
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

golang/scratch