CPython contribution docs reference missing /issuetracker page

[strugee]

https://cpython-devguide.readthedocs.io/pullrequest.html#licensing (and presumably other pages in this project) references https://cpython-devguide.readthedocs.io/issuetracker, but this page returns 404 Not Found.

(Moved from https://bugs.python.org/issue30001)

[Mariatta]

Thanks for the report @strugee
A new contributor is currently working on this issue, so I'm assigning this to myself to not duplicate anyone's effort.

[strugee]

@Mariatta that's phenomenal! Yay for more contributors 🎉