User-facing docs

Context

Need to write some user facing docs.

Task Description

• Revise the installation guide
• Getting started guide - ie, simple tutorial
• List of all the commands for reference
• Examples / demos
• Use Sphinx to render to a webpage, see #50 (closed)

Acceptance Criteria

• Link to rendered docs:
  • https://buildgrid.gitlab.io/buildgrid
  • https://buildgrid.build (for now)