Added a LICENSE.md to the docs folder. I also added explicit links to
the Creative Commons License.

Also notice that the license is in markdown format. I will be doing that
for the GPL license in the root folder when I can. Or maybe I will have
a plain text and a markdown version of each.

NOTE: The license changed in this commit. It used to be the Creative
Commons Attribution 3.0 License. Now, it's the Creative Commons
Attribution-NonCommercial-ShareAlike 3.0 Unported License. Because I am
the only contributor so far, I can do that.