Update README.md

Author: SableRaf

README.md

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 # processing4-javadocs
 This repository automatically generates the Javadoc for Processing 4 and hosts it on GitHub Pages
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+## License
+The Processing 4 reference is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License ([CC-BY-NC-SA-4.0](https://creativecommons.org/licenses/by-nc-sa/4.0/)).