Use uv as the recommended install method in docs

[Lynndabel]

What was wrong?

The install documentation recommended using standard pip only (python -m pip install libp2p), while the contributing guide and CI/CD use uv as the default tool.

This mismatch was confusing for contributors and users trying to mirror the CI environment and follow the recommended workflow.

How was it fixed?

• Updated docs/install.rst to recommend uv as the primary installation method, aligned with the contributing guide and CI.
• Added explicit uv-based steps:
  • Install uv via the official installer.
  • Create a virtual environment with uv venv venv.
  • Install from PyPI with uv pip install libp2p.
• Kept the previous pip-only flow as an “Alternative: using standard pip” section so users without uv can still install the package in the old way.
• No code or packaging logic was changed; this PR only updates documentation.

To-Do

• Clean up commit history
• Add or update documentation related to these changes
• Add entry to the release notes

Cute Animal Picture

closes #1175

[acul71]

Hello @Lynndabel thanks for this PR.
There are some lint/doc issues

make docs # or make linux-docs 
/home/docs/checkouts/readthedocs.org/user_builds/py-libp2p/checkouts/1178/docs/install.rst:2: WARNING: Block quote ends without a blank line; unexpected unindent. [docutils]
/home/docs/checkouts/readthedocs.org/user_builds/py-libp2p/checkouts/1178/docs/install.rst:63: WARNING: Block quote ends without a blank line; unexpected unindent. [docutils]
/home/docs/checkouts/readthedocs.org/user_builds/py-libp2p/checkouts/1178/docs/install.rst:63: CRITICAL: Title overline & underline mismatch.

try to fix the issues and ping if you find problems/need help

Also every PR must have a newsfragment doc file referring the issue look here https://github.com/libp2p/py-libp2p/blob/main/newsfragments/README.md

PS: In general before submitting a PR you can run make pr and make docs to see everything checkout