Streamline first-time-users experience

This involves both documentation and coding work, for instance:
- [ ] A fast `Getting started` video/gif should be present in the main page of the doc/README
- [ ] Documentation should be extended to ensure there's a linear sequence of steps to get started with each of the backends (independently of each other).
- [ ] Generate/publish a cheatsheet with the most important concepts and API (similar to [what we started here](https://cheatography.com/gonzalocasas/cheat-sheets/compas-fab/) but updated and ideally generated with LaTeX in this repo instead of using an external service)
- [ ] Consider if a `conda constructor` standalone installer package makes sense (https://github.com/conda/constructor)
- [ ] Add GH documents at different levels of complexity, instead of one that does it all. Ideally also create components out of the existing code (partially in progress already).