PEP 480: update distribution upload steps

[brainwane]

@mnm678 The section about PyPI users registering projects prior to uploading

peps/pep-0480.txt

Lines 380 to 395 in e2b198b

	The following outlines an automated signing solution that a new developer MAY
	follow to upload a distribution to PyPI:
	1. Register a PyPI project.
	2. Enter a secondary password (independent of the PyPI user account password).
	3. Optional: Add a new identity to the developer's PyPI user account from a
	second machine (after a password prompt).
	4. Upload project.
	Step 1 is the normal procedure followed by developers to `register a PyPI
	project`__.
	__ https://pypi.python.org/pypi?:action=register_form
	Step 2 generates an encrypted key file (private), uploads an Ed25519 public key
	to PyPI, and signs the TUF metadata that is generated for the distribution.

is now obsolete and needs to be updated before or as we re-start deliberations on this PEP.

Originally posted by @brainwane in #1693 (comment)

[mnm678]

This is partly addressed in #1711, although using Fulcio identities for developer key management, as proposed by @joshuagl here, would reduce the overhead for PyPI and further simplify these steps.

[brettcannon]

We try to keep this issue repository just for the repo itself and not the individual PEPs (too many of them for us to be a central clearinghouse for that sort of thing). I would email the PEP authors to find out where they want feedback to go.