arrow

MINOR: [Docs][Python] Small updates to the documentation about building pyarrow

I added some additional information and some changes to the documentation for building pyarrow from source. The changes are meant as a proposal to make this part of the documentation more clear and up-to-date and not as a final correction.

Closes #11505 from AlenkaF/pyarrow-build-docs

Authored-by: Alenka Frim <frim.alenka@gmail.com>
Signed-off-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>