[Proposal] Project Roadmap

This is a loose roadmap of our plans for major changes to Miniworld:

**June-August**:

- Documentation
- [x] Demo usage with reinforcement learning.

**Long-Term**:

- Code
- [ ] Update OpenGL version

The issue is a loose roadmap and only identifies a long-term code goal: update the OpenGL version. No file, test, or entry point is named; first clarify the target version and scope, then identify the affected rendering code and how completion will be verified.

Written by the indexing model from the issue text.