Hook to add license comments

[asottile]

[RonnyPfannschmidt]

the hook would have to be CI-aware so it would update in peoples homedir but sit it out on ci

[asottile]

I'm not sure it would need to be, depending on the scope here. for instance I would probably see this configured as:

    -   id: add-license
        args: [--license, apache, --owner, 'Anthony Sottile', --copyright-year, '2018']

and then it would ensure comments at the top of files like this

[jcpunk]

Personally, I'd love something that checks for SPDX tags.

[asottile]

there are existing hooks for this in https://pre-commit.com/hooks.html