Could you add a subcommand example?

[hnakamur]

First of all, thanks for a nice software!

I tried to create a subcommand example but I couldn't make it work as expected.
https://gist.github.com/hnakamur/3c8fba54b792536a196c

With Go's standard flag package, my example works as expected.
https://gist.github.com/hnakamur/2512fd35b8e0b41d2c08

So, could you add a subcommand example?
Thanks!