docs: fix dev server command in README (#848)

[Lasdw6]

This PR updates the README to correct the development server startup command from:

mcp dev server.py

to:

uv run mcp dev server.py

Motivation and Context

Per issue #848, the existing command in the README does not work and prevents users from launching the MCP development server. This change ensures the documented command is accurate and functional.

How Has This Been Tested?

N/A

Breaking Changes

N/A

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation update

Checklist

• [x] I have read the MCP Documentation
• [x] My code follows the repository's style guidelines
• [ ] New and existing tests pass locally
• [ ] I have added appropriate error handling
• [x] I have added or updated documentation as needed

Additional context

N/A