Add Copilot Instruction File

[mhellmeier]

🚀 Feature Request

Current Problem

GitHub added Copilot support, but the project misses further details for Copilot to work.

Proposed Solution

Create one or more Copilot instruction files to provide additional details and background information on the structure, code style, etc.

Additional Context

Best practices on instruction files:

• https://github.blog/ai-and-ml/unlocking-the-full-power-of-copilot-code-review-master-your-instructions-files/
• https://github.com/ljunggren/agentic-engineering/blob/main/agent-instructions-starter.md