Error when `pip install -r requirements-rtd.txt` for contributing to docs

[Paul Scemama]

When running the command pip install -r requirements-rtd.txt, an issue arises with use_2to3. This says it is due to setuptools>=58 breaking support for use_2to3. The changelog for setuptools notes:

"#2086: Removed support for 2to3 during builds. Projects should port to a unified codebase or pin to an older version of Setuptools using PEP 518 build-requires."

I resolved the issue by pip install setuptools==58 and then pip install -r requirements-rtd.txt.

Not entirely sure what the best option is to fix this.