Document setting limited-api via build option better

[lpsinger]

The limited-api option can only be set through pyproject.toml, not through the build config settings that you can provide on the command line to pip or python -m build.

Would you please consider supporting limited-api as a build config setting? I am using cibuildwheel to build a package that uses the limited API, but my build fails when it tries to install the build package and run my tests under pypy with the following error:

  ERROR: hpx-0.0.1-pp39-abi3-manylinux_2_17_x86_64.manylinux2014_x86_64.whl is not a supported wheel on this platform.

I would like to be able to customize the build so that it sets limited-api to false for PyPy, but I can't do this because limited-api is not a build config setting. Here's what I would like to do:

[tool.cibuildwheel]
config-settings.limited-api = true

# PyPy does not support the Python limited API.
[[tool.cibuildwheel.overrides]]
select = "pp*"
config-settings.limited-api = false