Clarify development setup: virtualenv, migrations, and tests

[lawie1425]

Problem: Development instructions are scattered and omit explicit commands for creating a virtual environment, installing dependencies, applying migrations, and running tests.

Proposed improvement: Add a consolidated "Development" section with explicit commands for python -m venv/pip install -r requirements.txt, database migration steps, and how to run the test suite (with example commands).

Expected benefit: New contributors can set up a reproducible dev environment and run tests reliably.

Files to change: README.md, optionally requirements.txt (if notes needed)

Suggested labels: docs, enhancement