Add the explicit Tidelift link.

Author: Julian

pyproject.toml

@@ -43,6 +43,7 @@ Documentation = "https://referencing.readthedocs.io/"
 Homepage = "https://github.com/python-jsonschema/referencing"
 Issues = "https://github.com/python-jsonschema/referencing/issues/"
 Funding = "https://github.com/sponsors/Julian"
+Tidelift = "https://tidelift.com/subscription/pkg/pypi-referencing?utm_source=pypi-referencing&utm_medium=referral&utm_campaign=pypi-link"
 Source = "https://github.com/python-jsonschema/referencing"
 
 [tool.coverage.html]