docs/guidance/publication.md: Add link to CoVE

[duncandewhurst]

Related issues
Add links to related issues here. Use keywords if you want an issue to be automatically closed when the PR is merged.

• Closes Data review tool admonition #194

Description
If the changes in the PR are not sufficiently explained by the related issues and commit messages, add a description here

Merge checklist

• If there are changes to network-schema.json, network-package-schema.json, reference/publication_formats/json.md, reference/publication_formats/geojson.md or guidance/publication.md#how-to-publish-large-networks, update the relevant manually authored examples:
  • examples/json/:
    • network-package.json
    • api-response.json
    • multiple-networks.json
    • network-embedded.json
    • network-separate-endpoints.json
    • network-separate-files.json
    • nodes-endpoint.json
    • spans-endpoint.json
  • examples/geojson/:
    • api-response.geojson
    • multiple-networks.geojson
• Run ./manage.py pre-commit to update derivative schema files, reference documentation and examples
• If you used a validation keyword, type or format that is not already used in the schema:
  • Update the list of validation keywords, types or formats in JSON Schema usage.
  • Add a field that fails validation against the new keyword, type or format to network-package-invalid.json.
  • Check that OFDS CoVE reports an appropriate validation error.
• If you added a normative rule that is not encoded in JSON Schema:
  • Update the list of other normative rules.
  • Add a field that does not conform to the rule to network-package-additional-checks.json.
  • Open a new issue to add an additional check to Lib Cove OFDS.
• If there are changes to examples/geojson/nodes.geojson or examples/geojson/spans.geojson, check and update the data use examples:
  • examples/leaflet/leaflet.ipynb
  • examples/qgis/geojson.qgs
• Update the changelog (style guide)