Add comprehensive GitHub Copilot setup instructions for new repositories

[Copilot]

The existing documentation assumed users already had GitHub Copilot properly configured in their repositories, but provided only a vague "Enable GitHub Copilot" instruction. This created a significant barrier for new users who needed foundational setup guidance before they could benefit from the ioBroker-specific template.

Changes Made

Added comprehensive "Prerequisites & Basic GitHub Copilot Setup" section with detailed step-by-step instructions covering:

• Subscription and Installation: Complete guide for VS Code, JetBrains IDEs, Vim/Neovim, and other editors
• Authentication and Validation: Clear steps to verify Copilot is working with code suggestions
• Repository Setup: Commands and validation steps for proper configuration
• Organization Permissions: Guidance for GitHub Copilot in organizational repositories
• Troubleshooting Table: Common issues and solutions for setup problems

Enhanced documentation flow by restructuring the README:

• Added prerequisite warnings with direct links to setup instructions
• Created Quick Reference checklist for experienced Copilot users
• Improved Integration Steps with setup verification commands
• Added post-integration validation and testing guidance

Updated template.md to reference the prerequisite setup guide, ensuring users understand the foundational requirements before attempting to use the ioBroker template.

Example of the improvement

Before:

3. **Enable GitHub Copilot**
   - Ensure GitHub Copilot is enabled for your repository
   - The instructions will automatically be used by Copilot when working in your codebase

After:

## 🛠️ Prerequisites & Basic GitHub Copilot Setup

### Step 1: GitHub Copilot Subscription & Installation
1. **Subscribe to GitHub Copilot**
   - Visit GitHub Copilot and subscribe to Individual or Business
   - Ensure your subscription includes your target repository

2. **Install GitHub Copilot Extension**
   - **VS Code**: Install the GitHub Copilot extension
   - **JetBrains IDEs**: Install from plugin marketplace
   [... detailed instructions continue]

The repository now provides a complete onboarding experience, guiding users from GitHub Copilot setup through successful ioBroker template integration, regardless of their prior Copilot experience.

Fixes #18.

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[Copilot]

Pull Request Overview

Addresses the significant setup barrier for new users by adding comprehensive GitHub Copilot prerequisites and setup guidance. Previously, the template assumed users had Copilot already configured, providing only vague "Enable GitHub Copilot" instructions.

• Added detailed "Prerequisites & Basic GitHub Copilot Setup" section with step-by-step instructions for multiple editors
• Enhanced documentation flow with prerequisite warnings, quick reference checklist, and validation steps
• Updated template.md to reference the setup guide for foundational requirements

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
template.md	Added prerequisite warning referencing the setup guide in README.md
README.md	Added comprehensive setup section with editor-specific instructions, validation steps, and troubleshooting
CHANGELOG.md	Updated with detailed feature additions for the new setup guide

[Copilot]

The anchor link #🛠️-prerequisites--basic-github-copilot-setup is repeated multiple times throughout the document. Consider extracting this to a constant or using a simpler, more reliable anchor format to avoid inconsistencies if the heading changes.