docs: clean up README setup guide

[CalLeeLQY]

Fixes #114

Summary

• Correct README setup prerequisites and configuration paths.
• Replace individual dependency install commands with pip install -r requirements.txt.
• Fix broken command examples, JSON fences, typoed headings, and duplicate deployment documentation.
• Clean up Markdown formatting so the README passes markdownlint with the project's existing disabled rules.

Verification

• git diff --check
• python3 -m py_compile gitHappens.py ai_code_review.py
• npx --yes markdownlint-cli --disable MD013 MD033 MD041 -- README.md