docs: add quick Windows demo and test instructions (attrs note)

[Denglish66]

Type of changes

• Bug fix
• New feature
• [ X] Documentation / docstrings
• Tests
• Other

Checklist

• I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate (see note about typos above).
• I've added tests for new code.
• I accept that @willmcgugan may be pedantic in the code review.

Description

Please describe your changes here. If this fixes a bug, please link to the issue, if possible.

Summary
This adds a short Windows PowerShell quickstart for Rich and a one-liner for running tests locally. It also notes that installing attrs may be required for a clean pytest -q run on a fresh env.

Why
New contributors on Windows may not know the PowerShell venv activation command, and first test runs can fail with ModuleNotFoundError: No module named 'attr'.

What changed

README: Quick Demo (Windows PowerShell) snippet

README: Run Tests (dev setup) snippet: pip install pytest attrs → pytest -q

Tested
Windows 11 + Python 3.13

Demo renders table and progress bar

Tests: 883 passed, 23 skipped on my machine

Notes
Happy to adjust placement/wording or move this into CONTRIBUTING if preferred.