[setup-sandbox] Script for fetching the go packages that are used by the scripts in this directory

Signed-off-by: Brad Figg <brad.figg@canonical.com>
[setup-sandbox] Make this script executable.

Signed-off-by: Brad Figg <brad.figg@canonical.com>
[README.md] 'install' instructions

Signed-off-by: Brad Figg <brad.figg@canonical.com>