please add missing license file + package.json entry

[GitMensch]

The easiest option for the license file: Just create a new file via GitHub giving it the name LICENSE - and you'll get a license chooser which also includes the appropriate license text. For package.json: add an entry "license" and place the appropriate SPDX license id there, see https://docs.npmjs.com/cli/v6/configuring-npm/package-json#license