docs: Update README.md

[isabelle-dr]

Add a section for projects based on this validator.

Please make sure these boxes are checked before submitting your pull request - thanks!

• [ ] Run the unit tests with mvn test to make sure you didn't break anything
• [x] Format the title like "feat: {new feature short description}" or "fix: {describe what was fixed}". Title must follow the Conventional Commit Specification (https://www.conventionalcommits.org/en/v1.0.0/).
• [x] Linked all relevant issues
• [x] Include screenshot(s) showing how this pull request works and fixes the issue(s)

[isabelle-dr]

@barbeau Do you know of any other?

[isabelle-dr]

Just added the other projects, the README.md now looks like this: