Document setup on macOS and Linux

[Abhay512]

The README was written on Windows. The commands are mostly portable but nobody has verified the full path end to end on macOS or Linux, and small things (activation script paths, cp vs copy, timezone configuration, pyarrow wheels on Apple Silicon) are exactly what stops a new contributor in the first ten minutes.

What to do

Run the full Getting started path on macOS and/or Linux and report or fix whatever breaks:

• Do all dependencies install cleanly? Apple Silicon in particular
• Does python -m tests.test_oneway pass?
• Does the dashboard build and run?
• Does docker compose up work, including the .env bind mount?
• Is anything about timezone handling different?

Acceptance

• README updated wherever the instructions were wrong or incomplete
• Platform-specific notes added where genuinely needed — without duplicating the whole guide per OS
• Say which OS and versions you verified on

Notes

"I followed it and everything worked on Ubuntu 24.04" is a genuinely useful contribution. Please still open the PR adding that note.