Explicit License

[grota]

Hi @webflo @weitzman @drumm
we recently forked this repo under our org, in an attempt to:

• manage on our end the code contributions (we liked tuutti's recent contribution)
• have a "backup strategy" to generate the resulting composer.json with the SA conflicts.

We have found no mention of the license in the code (only in the generated artifact).
We were wondering if you could make this project's license explicit as open source in order to avoid any legal issue by forking and using this project in our org.

[webflo]

I have little experience how to choose the right license :/ . Its GPL-2.0-or-later ok for everyone? Same as the generated files. I removed the file in commit c88123b so it wouldn't show up in Packagist. It was not intended to remove the license.

[grota]

:) I/we are not lawyers either, GPL-2.0-or-later is ok for us.
https://choosealicense.com/licenses/gpl-2.0/
https://spdx.org/licenses/GPL-2.0-or-later.html
Yeah I understand the removal of the top level composer.json, I'll try to create a PR with the facilities provided by github

[grota]

done in #44, the initial header I took from https://github.com/Automattic/jetpack/pull/7879/files