create a proper license file and statement

[maartentibau]

All the logos that are within this repository we don't hold a license on it, so this should be clearly mentioned in the README of the repo and also a specific LICENSE file.

The current LICENSE file in not appropriate.

Something we might be able to use is this one: https://github.com/gilbarbara/logos/blob/master/LICENSE.txt

Statement on the repo: All logos appearing on the site are the property of their respective owners.