Add NOTICE.txt in the repository

[julien-deramond]

A NOTICE.txt should be present at the root of this repository to list the parts belonging to Orange and that are not covered by the MIT license; i.e. logo, images, fonts.

An example can be found in https://github.com/Orange-OpenSource/ods-ios/blob/qualif/NOTICE.txt for iOS project that lists the images.

Another example can be found in https://github.com/Orange-OpenSource/Orange-Boosted-Bootstrap/blob/main/NOTICE.txt where logo, images and fonts are mentioned (specific case for Helvetica font used in web and probably not needed here).