With duplication, inconsistencies appears, such as:
- Poetry did not have a version check of sphinx-build;
- Poetry did not discern between git clone and fetching other
dependencies;
- Virtual environment and poetry documentation were different already;
- Build instructions sometimes used "qubes-doc" or "../qubes-doc".
New structure introduces sections to separate installation, lint and
build process.
Fix the "reStrucutredText" words. That's a good example on why it is
better not to label link when possible :)
There is other minor typos and inconsitencies (RST instead of rST).
