Help people learn how to download and contribute to the project.

Change-Id: I4b88b9b3872485ce78c7f6ea50596228afd82843
Reviewed-on: https://go-review.googlesource.com/49870Reviewed-by: Miguel Bernabeu <miguelbernadi@gmail.com>
Reviewed-by: Kevin Burke <kev@inburke.com>