docs: write initial README with project vision and roadmap

[Celz-Pch]

Goal

Give visitors a clear idea of what ZLearn is, why it exists, and where it's going.

Tasks

• One-line pitch
• Project goals (educational? performant? both?)
• Build & install instructions
• Minimal usage example (even if aspirational)
• Roadmap section linking to milestones
• License badge and contributing link

Acceptance criteria

• A first-time visitor understands the project in under 60 seconds.