Add a license

I would like to run your code, but I legally can't without a license to do so. Please add a license to your code. Since this is server-side code, the [AGPLv3 license](https://choosealicense.com/licenses/agpl-3.0/) is a good choice, otherwise, if you want permissive, [Apache 2.0](https://choosealicense.com/licenses/apache-2.0/) is too.