Add Developer Guide Section to Docs

[ananos]

We currently lack a dedicated section for developers who want to contribute to the project. This can be added as a separate file and linked from the main README.

Details

We should:

• Create a new file docs/development.md or section
• Document setup instructions, including cloning, installing dependencies, running tests, and contributing guidelines
• Include a brief explanation of the codebase layout.

This will improve contributor onboarding and reduce setup friction.