Organize docs with single lefthand sidebar

[MrPowers]

Can we please add a single lefthand navigation to the docs? Something like this:

Home
Installation
Usage
  Overview
  Loading a Delta Table
  Examining a Delta Table
  Querying a Delta Table
  Managing a Delta Table
  Writing Delta Tables
API Reference

[r3stl355]

This can be done but it will also change how the rest of the pages look, e.g top navigation menus. This is all driven by the theme. Currect version is using material which is popular at the moment. We can choose a style and make our own modifications but we need to choose the overall desired design before making changes to sections.

[MrPowers]

I am moving the installation guide to the Usage section that will fix this issue: #1875