Add key copyrightStatement to sources #127

[Ludee]

Summary of the discussion

This old Blog post suggests a way of storing a link to the copyright information. This is very useful and has been missing.
Source: https://frictionlessdata.io/blog/2018/03/27/applying-licenses/#provide-additional-license-information

There is a suitable ontology from the Open Data Institut (ODI):
Original source: https://theodi.org/insights/guides/publishers-guide-to-the-open-data-rights-statement-vocabulary/
http://schema.theodi.org/odrs/

This is the corresponding property:
odrs:copyrightStatement

A link to a document that includes a statement about the copyright status of the content of a dataset. The web page might include both a copyright notice for a dataset, and any relevant guidance for re-users.

-> Badge: Silver

Type of change (CHANGELOG.md)

Added

• Add key copyrightStatement to sources (#162)

Workflow checklist

Automation

Closes #127

PR-Assignee

• 🐙 Follow the workflow in CONTRIBUTING.md
• 📝 Update the CHANGELOG.md
• 📙 Update the documentation

Reviewer

• 🐙 Follow the Reviewer Guidelines
• 🐙 Provided feedback and show sufficient appreciation for the work done

[jh-RLI]

LGTM