PEP 810: Add link to demo (#4646)

Author: pablogsal

peps/pep-0810.rst

@@ -497,6 +497,9 @@ Reference Implementation
 A reference implementation is available at:
 https://github.com/LazyImportsCabal/cpython/tree/lazy
 
+A demo is available (not necessarily synced with the latest PEP) for
+evaluation purposes at: https://lazy-import-demo.pages.dev/
+
 Bytecode and adaptive specialization
 -------------------------------------