Update Python versionin README to 3.11 and use uv for setup

[cnaples79]

Summary

• Updated README to reflect Python 3.11 as the officially supported version
• Replaced venv usage example with uv (modern Python environment manager)
• Added cross-platform activation commands

Changes Made

• Line 46: Changed "supports Python3.7 through Python3.11" to "officially supports Python3.11"
• Lines 47-51: Replaced venv example with uv commands:
  • Added link to uv GitHub repository
  • Updated environment creation command to use uv venv --python 3.11
  • Included both Unix/macOS and Windows activation commands for clarity

Before

Augur supports ```Python3.7``` through ```Python3.11``` on all platforms. ```Python3.12``` and above do not yet work because of machine learning worker dependencies. On OSX, you can create a ```Python3.11``` environment, by running:

$ python3.11 -m venv path/to/venv

After

Augur officially supports ```Python3.11``` on all platforms. ```Python3.12``` and above do not yet work because of machine learning worker dependencies. We recommend using [uv](https://github.com/astral-sh/uv) to manage your Python environment:

$ uv venv --python 3.11 $ source .venv/bin/activate # On Unix/macOS $ .venv\Scripts\activate # On Windows

Benefits

• Clearer documentation that Python 3.11 is the officially supported version
• Modern tooling recommendation (uv is faster and more reliable than venv)
• Better onboarding experience with explicit activation commands for both platforms

Fixes #3441