Link to typing spec rather than PEP-561 (#15461)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Author: droppingbeans

README.md

@@ -38,7 +38,7 @@ you can install the type stubs using
 $ pip install types-html5lib types-requests
 ```
 
-These PyPI packages follow [PEP 561](http://www.python.org/dev/peps/pep-0561/)
+These PyPI packages follow [the typing spec standards](https://typing.python.org/en/latest/spec/distributing.html)
 and are automatically released (up to once a day) by
 [typeshed internal machinery](https://github.com/typeshed-internal/stub_uploader).