Add headers check

In this repo, there are few enough files (and likely wont be many more) that I think a pre-commit hook should work.

If there is some built-in python way to do this, do that. If not, a script is fine. See https://github.com/vinyldns/vinyldns/blob/master/bin/add-license-headers.sh for an example of how we scripted this for the non-scala files in the api