Unifying packaging.python.org with pypa.io, possibly other PyPA docs too

We have a few web properties that represent "Python Packaging":

• https://packaging.python.org (this repo, fairly well maintained)
• https://pypa.io (https://github.com/pypa/pypa.io, infrequently updated)
• Various project-specific docs:
  • https://pip.pypa.io/
  • https://virtualenv.pypa.io/
  • https://warehouse.pypa.io/
  • etc

I'd like to propose unifying at least the first two, by rolling pypa.io into packaging.python.org, and making packaging.python.org more of a "landing page for Python packaging" (which would mostly include the existing content, but also content about what the PyPA is, brought from pypa.io)

I'd also like to move anything that's not directly related to developing PyPI and more related to using PyPI (like https://warehouse.pypa.io/api-reference/index.html) to packaging.python.org, and generally make it a policy that:

• packging.python.org is for end users
• Warehouse docs are for Warehouse contributors and maintainers

(This would be easy because the Warehouse docs are mostly for maintainers/contributors, and very little for end-users.)

This leaves other project-specific docs, like the pip docs, which are mostly for end-users, but also contain some development guides. Some possibilities:

• Nothing changes, they continue to live at *.pypa.io but pypa.io redirects to packaging.python.org
• They live at *.packaging.python.org instead
• Or, a more extreme version of this would be to (somehow?) unify all project-specific end-user documentation under packaging.python.org

I'm not sure the last one is a good idea or even technically possible, but I do think giving end-users a one-stop-shop for user guides, tutorials, etc is something worth working towards.

(cc @brainwane @pradyunsg @ewdurbin @webknjaz @pfmoore @uranusjr @gaborbernat)

Start by reviewing the existing content in packaging.python.org, pypa.io, and the Warehouse documentation, especially warehouse.pypa.io/api-reference/index.html. Map which material targets end users versus Warehouse contributors and maintainers, then document the proposed information architecture and migration scope. This issue is done when the sites and documentation boundaries have an agreed plan.