Add licence file

LICENCE.md

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+# Licence
+
+Unless otherwise specified, everything in this repository is covered by the following licence:
+
+[![Creative Commons Attribution 4.0 International Licence](http://i.creativecommons.org/l/by-sa/4.0/88x31.png)](http://creativecommons.org/licenses/by-sa/4.0/)
+
+***Robo Butler*** by the [Raspberry Pi Foundation](http://www.raspberrypi.org) is licensed under a [Creative Commons Attribution 4.0 International Licence](http://creativecommons.org/licenses/by-sa/4.0/).
+
+Based on a work at https://github.com/raspberrypilearning/robobutler