Create LICENSE

[fm75]

Fixes #26

[takluyver]

I'm not sure the BSD license makes sense for this, as it's teaching materials rather than code.

We generally say that code and examples are BSD, and docs/diagrams/etc are CC-BY. Here's the page from IPython, for instance:
http://ipython.readthedocs.io/en/stable/about/license_and_copyright.html

[fm75]

@jzf2101 - OK. We did many PRs as part of a sprint after jupytercon. I think it would be best to let Jessica work out the details on this PR.