[DOCS] Import sections of JuliaCall docs

[MilesCranmer]

It would be useful to import sections of the JuliaCall docs so things are presented up-front rather than the user needing to find it. For example I think all the environment variables https://juliapy.github.io/PythonCall.jl/stable/juliacall/#julia-config could be displayed on the PySR docs too.

(Would help prevent, e.g., #600)