Deprecate old RO-Crate validator package

[elichad]

This one https://pypi.org/project/rocrateValidator/ is no longer developed. It's on PyPI as https://pypi.org/project/rocrateValidator/ and could be mistaken for the CRS4 validator (roc-validator on PyPI).

• [ ] add message to README with link to the CRS4 validator
• [ ] make a final release and publish it to PyPI so the README update shows up there

[elichad]

Could also consider renaming the old package entirely to free up the name rocrate-validator for CRS4

[stain]

I renamed https://github.com/researchobject/ro-crate-validator which was the .NET package, it is now https://github.com/ResearchObject/ro-crate-validator-dotnet and in Archived state. There should not be many incoming links to this as it was only ever a draft design so that repository name could be repurposed if the crs4 validator moves to this organisation.

Will also archive https://github.com/ResearchObject/ro-crate-validator-py once I've got a last-seen release pushed to pypi so it gets a README file shown on that side.