License this code

[iansan5653]

Hello, I'd like to adapt your work into my Google Apps Script template repository, but I can't legally do that because the code is not licensed for reuse.

Could you add a license.md file with a formal license? Here's details on how to do that: https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/adding-a-license-to-a-repository

[ianhyzy]

Bumping this

[ericanastas]

@iansan5653 @ianhyzy 

Done! a3dd7d1