Change the license

[rickecon]

We need to change the license in this repository to the Creative Commons Attribution Non Commercial Share Alike 3.0 license. The current license in the repo is the BSD-3-Clause License. The Creative Commons license listed above is the one used by the Pro-Git book which comes in hard copy but is also freely available online. I think this is the model we want to follow for this Jupyter Book that is exclusively book content, not a piece of software, code, or model.