Add a link to PyPI FAQ to clarify what per-project token is. (#14242)
<!--
Thank you for contributing to uv! To help us out with reviewing, please
consider the following:
- Does this pull request include a summary of the change? (See below.)
- Does this pull request include a descriptive title?
- Does this pull request include references to any relevant issues?
-->
## Summary
This change adds a link to PyPI FAQ about API tokens on the package
publishing guide page. To me it wasn't clear what are meant in this
section of the docs and it required a little bit of research. Adding
explicit link might help beginners.
<!-- What's the purpose of the change? What does it do, and why? -->
Co-authored-by: Dmitry Bychkov <dbychkov@alarislabs.com>