Since this project is a compilation of my own things mixed with ideas
and notes I learned from others, it makes sense that I restrict the
license so others cannot try to sell content from this project.

See:

• https://creativecommons.org/licenses/by-nc-sa/4.0/
• https://creativecommons.org/2014/01/07/plaintext-versions-of-creative-commons-4-0-licenses/
• https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode.txt