Improve usability of config reference section

[jcfr]

Following discussion with @LecrisUT , we suggest to improve the config reference section to:

• describe how to use each in the context of pyproject.toml, config-settings and environment (where applicable)
• include a link back to the main documentation if relevant

[jcfr]

Ideally, it would also be nice to crosslink entry with the schema documentation but that may be challenging given the current table formatting