Add comprehensive download and setup instructions to Java Homework README

[Copilot]

This PR addresses the common question "how do I download this folder?" by adding detailed download and setup instructions to the Java Homework README.

Changes Made

Enhanced README.md

• Added "How to Download This Folder" section with 4 different download methods:
  • Git clone for the entire repository
  • GitHub CLI option for advanced users
  • ZIP download from GitHub web interface
  • Individual file download instructions
• Added Prerequisites section specifying Java JDK 8+ requirement
• Added "How to Run After Downloading" section with:
  • Quick start commands for Linux/Mac and Windows
  • Manual compilation instructions as fallback
  • Clear step-by-step setup process
• Enhanced Folder Structure section with detailed file descriptions

Added .gitignore

• Prevents compiled Java class files (*.class) from being committed
• Includes common IDE and OS-generated files to ignore

Problem Solved

Previously, users had no guidance on how to download or set up this Java Map Editor project. The README now provides multiple clear paths for different user preferences and technical skill levels, making the project accessible to anyone wanting to run the Map Editor locally.

The instructions have been tested to ensure the Java compilation works correctly with the provided commands.

Original prompt

On Java Homework, how do i download this folder

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