Use pyproject.toml instead of setup.cfg and cleanup development notes in readme

[MartinBoge]

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[tbg-delegate]

Update on part of this for @LauJohansson, @MartinBoge:
Tagging @RadekBuczkowski to support my claim.
I recently tried changing from setup.py(nearly empty)+setup.cfg to setup.py(nearly empty)+pyproject.toml entirely and building using this.
It works fine locally on Windows, but fails on Ubuntu 22.04 (primary OS for GitHub Actions and Databricks).

My experience can be replicated using WSL, Python 3.10 (native) and setuptools. Even updating pip, setuptools and wheel did not help with the issue.

I suggest we close this issue and maybe revisit at some point in the future.