docs: add AGENTS.md with LLM contribution guide

This commit introduces AGENTS.md, a comprehensive guide outlining conventions and project context for language model (LLM) contributions to the awesome-go repository. The document details project structure, coding guidelines for Go and JavaScript, CI/testing expectations, and documentation standards. It aims to ensure consistency, quality, and clarity for both human and automated contributors.

Signed-off-by: Avelino <[email protected]>