add license to readme

Author: tobihagemann

README.md

@@ -36,3 +36,7 @@ Other scripts can be found in `package.json`.
 ## Deployment
 
 Deployed to [docs.cryptomator.org](https://docs.cryptomator.org) via GitHub Pages from the `main` branch.
+
+## License
+
+This documentation is licensed under the [Creative Commons Attribution-ShareAlike 4.0 International License (CC-BY-SA 4.0)](LICENSE.txt).