Add license file about python3statement.github.io

[takluyver]

I'd say the text content is CC-BY, and any code is MIT or similar, or even public domain.

Logos... myeh, I'd be inclined to say that life's to short to define the exact legal status of them. We check when people add a project that they're a maintainer or they have the support of the maintainers, so I think we can be satisfied that the projects are happy for us to use their logos. Logos are covered by trademark law as well as copyright, and that's got a load of different complexities.

[Carreau]

Agreed with TK. CC-BY, and public domain for code.

[takluyver]

@pganssle does #110 look OK to you? I don't really know how to apply a mixture of licenses, so it's not a simple LICENSE file.

[takluyver]

Closed by #110.