Added information about EAN-13

[larshalvoraam]

Propose this text, to let users know more about how ot start using EAN13 Most retail products use EAN-13 barcodes also named GTIN: Global trade Identification Number. They cannot be made up without proper authorization and you need a company number as a prefix. Find more information at https://www.gs1.org/standards/id-keys/gtin GS1 have assosiated organisation world wide, where you can apply for your company number. There is a fee for your company number.

[robodoo]

Pull request status dashboard.