Add comprehensive README documentation

[Copilot]

The repository lacked any documentation for setup and usage.

Changes

• Added README.md with project overview, real-time collaborative document editor built on Node.js, Socket.io, and MongoDB
• Installation instructions: Prerequisites, dependency installation, MongoDB configuration
• Socket.io events documentation: Client-server event flow (get-document, send-changes, save-document, load-document, receive-changes)
• Architecture details: Project structure, database schema, controller functions
• Security guidance: Environment variable usage for credentials, avoiding hardcoded passwords in production

Key Sections

• Features: Real-time collaboration, auto-save, WebSocket communication
• Tech stack: Node.js, Socket.io, MongoDB, Mongoose
• API: Document CRUD operations via Socket.io events
• Configuration: Port (9000), CORS (localhost:3000), MongoDB connection

Original prompt

Create a readme for this a basic one

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.