Added README for cc.github.io repo.

Author: kgodey

assets/README.md

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+# Creative Commons Open Source
+
+⚠️ DO NOT MODIFY THIS REPOSITORY! 
+
+These are the static files for [Creative Commons Open Source](https://creativecommons.github.io/). The files are automatically built via CI from the source files in the [creativecommons.github.io-source](https://github.com/creativecommons/creativecommons.github.io-source) repository.