Update README.md

Author: mre

README.md

@@ -2,3 +2,6 @@
 
 This repo contains bits and pieces of fine art, that might come in handy in a future "Hello Rust!" episode.
 
+# License
+
+Unless otherwise state, all artwork is licensed as [Creative Commons Attribution Share Alike 4.0](https://choosealicense.com/licenses/cc-by-sa-4.0/).