Add visual of suggested folder structure to Quick Start Guide

[sfregosi]

https://sfregosi.github.io/agate-public/get-started.html#set-up-folder-structure

Add visual of suggested folder structure:

├── sgXXX_XXX_LocYEAR (mission folder)
  ├── piloting (optional subdir)
    ├── flightStatus
    ├── basestationFiles
    └── profiles