Add comprehensive README.md file for FitMap project

[Copilot]

This PR adds a comprehensive README.md file to address the missing project documentation. The README provides complete guidance for developers to understand, set up, build, and deploy the FitMap fitness mapping application.

What's Added

The README includes:

• Project Overview: Clear description of FitMap as a fitness mapping application built with Java Google Cloud Functions and Firebase authentication
• Architecture Documentation: Detailed breakdown of the two main components:
  • Backend functions (Java 11, Spring Boot, Google Cloud Functions, Firestore)
  • Frontend authentication (Firebase Auth UI, Firebase Hosting)
• Development Setup: Step-by-step instructions for local development including Java 11, Maven, Docker, and Google Cloud SDK requirements
• API Documentation: Complete documentation for the SetRoles function endpoint including request/response formats
• Deployment Guide: Instructions for deploying both backend functions to Google Cloud and frontend to Firebase Hosting
• Testing Guidelines: Information about the comprehensive test suite using JUnit 5, Mockito, and AssertJ
• Troubleshooting Section: Common issues and solutions, particularly around Java version compatibility

Key Features

• Complete project structure diagram showing the organization of functions and web-auth directories
• Docker-based local development setup with service scripts for easy management
• Production deployment instructions for Google Cloud Functions (southamerica-east1 region)
• Prerequisites and environment setup with specific version requirements
• Contributing guidelines and development best practices

The documentation ensures that new developers can quickly understand the project's purpose, set up their development environment, and contribute effectively to the codebase.

Fixes #1.

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