[doc] Add PATH refresh to README to fix 'command not found' error

[PluviaLiu]

I just tried setting this up on macOS and hit a small snag.

If you run the curl install and then uv venv immediately (like the README suggests), it throws a command not found error. This is because the shell needs a refresh to recognize the new path.

To make it smoother for Mac users, maybe add a source line in the middle? Something like:

# Install uv (if not already installed)
# macOS/Linux:
curl -LsSf https://astral.sh/uv/install.sh | sh
source $HOME/.local/bin/env    # <--- ADD THIS: Refreshes PATH for the current session

# Create virtual environment
uv venv

# Activate virtual environment
# macOS/Linux:
source .venv/bin/activate
# Windows:
# .venv\Scripts\activate

# Install Python dependencies
uv sync

This ensures a smoother "one-click" style installation for mac users. Hope this helps ：）