Basic documentation that's missing from the website

[bugarela]

Hello

This is a website revamp ✨. I reorganized the whole structure, and added several new pages:

• Introduction > Why?
• Introduction > Quint Basics
• Introduction > Language Basics
• Using specifications > Checking properties
• Using specifications > Model-based Testing
• How the tools work > Model checkers
• How the tools work > Understanding the simulator

You can check a preview here: https://gabriela-basic-docs--quint-docs.netlify.app/docs/getting-started

I'm looking for two things here:

1. High level review, making sure there is nothing too out of place. Considering that the current website has zero information about some of the stuff I'm adding, I'm looking for merge this soon and not go into too much nitpicking while the current state is lacking so much.
2. Any sort of feedback to be implemented on the future.

(1) is higher priority than (2) at this point, and we can always iterate after merging.