Add comprehensive README file for mlenv project

[Copilot]

This PR adds a comprehensive README.md file to properly document the mlenv machine learning environment toolkit. The previous README was empty, making it difficult for users to understand the project's purpose and how to use it.

Changes Made

New README.md

• Project Overview: Clear description of mlenv as a comprehensive ML environment with popular AI/ML libraries
• Features Section: Highlights key capabilities including PyTorch, Hugging Face transformers, OpenCV, FastAPI, Gradio, and more
• Installation Instructions: Multiple installation methods (uv, pip, Docker) with step-by-step commands
• Quick Start Guide: Simple example using the included hello.py script
• Dependencies Table: Organized overview of key packages and their purposes
• Development Guidelines: Instructions for testing, code style, and Docker development
• CI/CD Documentation: Information about GitHub Actions workflows
• Contributing Guidelines: Standard workflow for contributors

Updated pyproject.toml

• Replaced placeholder description with meaningful project description that matches the README

Key Features Documented

The README now properly explains that mlenv provides:

• Deep learning with PyTorch ecosystem
• NLP capabilities with Hugging Face transformers
• Computer vision with OpenCV and Ultralytics (YOLOv8+)
• Web interfaces with FastAPI and Gradio
• Data analysis tools (pandas, numpy)
• Financial analysis (mplfinance)
• Modern packaging with uv
• Containerized deployment with Docker

The documentation is structured to help users quickly understand the project, install it using their preferred method, and start using it effectively for machine learning projects.

Fixes #1.

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