How does pattern work?

Hello there,

I'm using this on `nancy`, and more or less, great tool!

However, it's a bit too nuclear with the `.` pattern, and adding licenses to files that we need to exclude (primarily GitHub templates, but we also don't really need licenses on files that really don't have IP (Dockerfile, gorelease.yml, etc...), so I was looking at using the pattern to basically only check and apply to `**/*.go` files, and maybe a couple others here and there. There isn't really much documentation I can see on `pattern`, so I figured I'd ask about usage, and then send y'all a PR with it included in the README for other goofballs like myself!

Cheers!