Make the docs page better structured

[matteobachetti]

The old page was basically a TOC, kind of unstructured (e.g. the getting started drown between installation and many advanced applications):

As a side effect, the left-hand side menu was basically uninformative.

I made a few things: I put the installation instructions and the main features directly in the first page. Then, I split the TOC into different parts, divided by level. As a result, also the left-hand side menu is richer, giving more information to new users.


Also, I made the docs only CI work... I separated that part in another PR: #749

[codecov]

Codecov Report

Merging #748 (1b01cc3) into main (7844fc8) will decrease coverage by 0.06%.
Report is 5 commits behind head on main.
The diff coverage is n/a.

❗ Current head 1b01cc3 differs from pull request most recent head 2054c89. Consider uploading reports for the commit 2054c89 to get more accurate results

@@            Coverage Diff             @@
##             main     #748      +/-   ##
==========================================
- Coverage   97.13%   97.08%   -0.06%     
==========================================
  Files          42       42              
  Lines        7929     7929              
==========================================
- Hits         7702     7698       -4     
- Misses        227      231       +4     

see 2 files with indirect coverage changes

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[dhuppenkothen]

Much better! Yay!