[Docs] dependency_links removal documentation

Summary

Thank you for your work on this package. I'll admit I'm pretty new to the python ecosystem, so I apologize if I'm off base here.

I was reading the steuptools documentation of dependency_links of the latest version. At the top, it has a warning that "Dependency links support has been dropped by pip starting with version 19.0 (released 2019-01-22)." I was confused about what to do next, since I needed to specify a link to a GitHub repo. I would have found it useful if there were a link to the current documentation on how to achieve the same result with current versions of pip.

I found this link that had a bit more up to date information: https://setuptools.pypa.io/en/latest/userguide/dependency_management.html#direct-url-dependencies. It doesn't line up with what I found at https://packaging.python.org/en/latest/specifications/dependency-specifiers/#examples, though, which uses a zip address. I'm not sure what the best edit would be.

By the way, the issue template here says there's a "View on GitHub" link on every documentation page, but I was unable to find that on pages on the documentation site.

OS / Environment

Irrelevant.

Additional Information

I think adding to these docs can help developers understand how to solve a problem with less digging and be more up to date with the specs.

Code of Conduct

• I agree to follow the PSF Code of Conduct

Start by comparing the setuptools dependency_links documentation with the linked direct URL dependencies guidance and the packaging.python.org dependency-specifiers examples. Clarify the current supported approach and link to authoritative documentation, while checking whether the reported missing “View on GitHub” link is also within scope. Done means the docs give developers an unambiguous path forward.