docs: Fix manual install command in quickstart

[jacobsimionato]

Updates the quickstart guide to use pip install . instead of pip install -r requirements.txt, as the project uses pyproject.toml.

Fixes #424

[gemini-code-assist]

Code Review

This pull request correctly updates the manual installation command in the quickstart guide to use pip install ., which is appropriate for a project configured with pyproject.toml. However, I've identified a significant inconsistency in the surrounding documentation. The guide suggests Python 3.10+ is sufficient, but the project requires Python 3.13+. This will cause the installation to fail for users with an intermediate Python version. I've added a high-severity comment to highlight this issue, which should be addressed to ensure the quickstart works as intended for all users.

[gemini-code-assist]

While pip install . is the correct command for this project, it will fail for users with a Python version between 3.10 and 3.12. The project's pyproject.toml requires Python 3.13 or newer (requires-python = ">=3.13"), but a comment in this code block suggests 3.10+ is sufficient. To prevent installation errors, the Python version mentioned in the guide should be updated to 3.13+.