Add direct installation via uv from GitHub repository

[xsa-dev]

Currently, the installation guide suggests cloning the repository and installing dependencies manually, which can be inconvenient for users who just want to try or integrate the library quickly.

This update proposes adding an alternative installation method using uv, which allows installing the package directly from the GitHub repository without manual cloning:

uv pip install git+https://github.com/XSpoonAi/spoon-core.git@main