Correct licensing of the website

As stated on the "Applying Licensing" page:

https://www.apertis.org/policies/license-applying/

Apertis code, including build scripts, helpers and recipes, is
primarily licensed under the Mozilla Public License Version 2.0.
Images (such as icons) and documentation in Apertis are licensed
under the Creative Commons Attribution-ShareAlike 4.0 International
(CC BY-SA 4.0) license.

The website is (pretty much) entirely documentation, so should be licensed as CC BY-SA 4.0, however the repository has mistakenly been given an MIT license. Correct this by adding the correct license text.

Signed-off-by: Martyn Welch martyn.welch@collabora.com