docs: refresh README guidance

[jakob1379]

The current readme does not do this project justice. This PR tries to improve clarity, navigation, development workflow and the general structure of it.

The changes include:

• Rewrites the README with a clearer overview, installation flow, first steps, and
  development guidance.
• Documents the package/import naming distinction: res-wind-up on PyPI and wind_up
  in Python.
• Adds GitHub admonitions for development workflow guidance

Verification:
All commands in the readme have been run and verified

• Verified documented install commands with uv and pip.
• Verified optional example dependency install commands.
• Verified documented Python imports.
• Ran uv sync --all-extras --dev.
• Ran uv run poe all-fast.
• Ran uv run poe all.
• Ran uv run poe lint-check.
• Ran uv run poe test-fast.
• Checked Markdown code fences and local README links.