Copyright or software licenses for SWEET ontologies

[rduerr]

SWEET ontology files and other documents under this repository should have copyright and/or software licenses attached.

As examples, the schema.org schema is licensed under Creative Commons Attribution-ShareAlike License (version 3.0). Meanwhile W3C documentation about ontologies such as DCAT-2 are copyright W3C and ontologies are licensed using https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document. In Agroportal, of 109 ontologies, 69% are
https://creativecommons.org/licenses/by/4.0/ (or http equivalent), 7% are https://creativecommons.org/publicdomain/zero/1.0/, and the rest are 'other'.

Recommend using dc:license (http://purl.org/dc/terms/license) with value https://creativecommons.org/publicdomain/zero/1.0/ for the ontology files.