Add Python and ESRI guidance to Demographics Use Case page

See https://cawaterboarddatacenter.github.io/equity-data-handbook/use-cases/demographics.html#python-data-integration-example
general structure of sections should reflect R section structure (e.g. set up, collection, processing, etc.)

Open the Demographics Use Case page at the linked Python data integration example and compare its current structure with the R section. Add the Python and ESRI guidance using corresponding setup, collection, and processing sections; done means the new guidance follows the R section’s general structure.

Written by the indexing model from the issue text.