Doc PyPI sdist and GitHub tag options

There are of course pros and cons of PyPI sdists vs. GitHub tags. In some cases, the right choice varies depending on what the package is. In any event, we should add a note to the docs laying out these options and their implications along with any gotchas so packagers can choose what fits their needs.

Side note: Having a strong feeling of déjà vú. May have duped myself with this issue, but couldn't find the other one when searching. So sorry if I opened this yet again (maybe it's an indication we should start writing 😉).