Mark copyright/licenses

[rpavlik]

(At least for code but ideally for everything) As an open source consultancy we're well attuned to the requirements of licenses. It would be good if you could mark at least the example code with copyright and license data (SPDX-License-Identifier preferred). I recommend the https://reuse.software standard, because it's straightforward and comes with a nice tool you can even have in ci, reuse lint