fix: enhance existing authentication docs

[lwasser]

closes #821

This is a small update to the authentication page. it adds

✅ subheadings for easier skimming
✅ a breakout on 2FA as requested in #821
✅ a bit of clarification throughout.

I have two significant questions.

1. like others mentioned in that 821 i found that even with my username stores in the toml file, hatch still asked for it.
2. The order of precedence for username vs password is different in this file. I didn't touch this but i wonder if that is actually the case?

IN other words, if i just enter credentials manually using -u and-auth will hatch still try to override with the .pypirc file if it finds it? i'm now convinced that order is actually correct but i also haven't dug into the code yet.

[pitrou]

Suggested change

	1. a username (e.g. `__token__` for PyPI)
	1. a username (e.g. `__token__` for PyPI to select two-factor authentication aka. 2FA)

[pitrou]

Suggested change

	2. a token value or other form of trusted authentication from the index (PyPI)
	2. a password, token value or other form of trusted authentication for the package index

[pitrou]

Suggested change

	To publish to an index such as PyPI or TestPyPI you need two things:
	To publish to a package index such as PyPI or TestPyPI you need two things:

[pitrou]

Hi @lwasser , I just posted a couple of comments in the hope of making the help more explicit and easier to understand. Feel free to approve these changes or not :)