Add LICENSE file

[brylie]

After removing the dependency on AmCharts (issue #1), this project can be offered under an open source license.

Choose a license for the project, and add the license file to the root of the repository. The conventional name for the file is LICENSE or LICENSE.md.

[synw]

I did not realize that there is not even a license, its really an old project that comes back to life. I'll add the MIT license when we will have removed the Amcharts dependency