Creative Commons Attribution 4.0 International (CC BY 4.0)

You are free to:

* **Share** — copy and redistribute the material in any medium or format.
* **Adapt** — remix, transform and build upon the material for any purpose,
  even commercially.

Under the following terms:

* **Attribution** — You must give appropriate credit, provide a link to the
  licence and indicate if changes were made. You may do so in any reasonable
  manner, but not in any way that suggests the licensor endorses you or your
  use.
* **No additional restrictions** — You may not apply legal terms or
  technological measures that legally restrict others from doing anything the
  licence permits.

Full licence text: https://creativecommons.org/licenses/by/4.0/legalcode