PEP 740: add PyPA spec

Signed-off-by: William Woodruff <william@yossarian.net>

Author: woodruffw

peps/pep-0740.rst

@@ -14,6 +14,8 @@ Post-History: `02-Jan-2024 <https://discuss.python.org/t/pre-pep-exposing-truste
               `29-Jan-2024 <https://discuss.python.org/t/pep-740-index-support-for-digital-attestations/44498>`__
 Resolution: `17-Jul-2024 <https://discuss.python.org/t/pep-740-index-support-for-digital-attestations/44498/26>`__
 
+.. canonical-pypa-spec:: :ref:`packaging:index-hosted-attestations`
+
 .. canonical-doc:: `PyPI - Digital Attestations <https://docs.pypi.org/attestations/>`__
 
 Abstract