enhancement: refactor documentation

[giovanni-vaccarino]

Description

This PR fixes #12, by reorganizing the documentation under docs/ in many .md files, instead of a single bloated README.md. In particular the directory structure inside docs/ mirrors the codebase structure. A setup.md have been added to handle the installation guides for both Linux and Windows OSs. The README.md now contains only the basic information about the documentation, explains how to run the basic flows using the targets of the Makefile, and refer to other documentation files for further details.

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[giovanni-vaccarino]

@berviantoleo I've included a new workflow for windows, as you suggested in #12. Should I also run the backend tests in that workflow, or its purpose is only to verify the installation with requirements-cpu.txt?

[berviantoleo]

@berviantoleo I've included a new workflow for windows, as you suggested in #12. Should I also run the backend tests in that workflow, or its purpose is only to verify the installation with requirements-cpu.txt?

I don't think we need that for backend tests. Just for verifying the requirements file.