Add more linking metadata (through ACDD?)

Other IDs should be added (through the ACDD metadata although these are not ACDD?):

• Research Organization Registry (ROR), https://ror.org/
• wikidata, https://www.wikidata.org/
• geoname ID, https://www.geonames.org

We might not use them all, but some (like ROR) could be very useful...