Example project fixes and readme additions

[jeffward01]

Changes:

• Fixed the type from Unet to Upscalers in the example appsettings.json folder
• Fixed example 2 in the console app
• Added readme instructions for 'how to get started' with the example app
• Added an experimental script to auto-download the required models for the example project to an onnx-models/ directory
  • Also added this folder onnx-models/ to git ignore
• Added short FAQ section with some common configuration errors

[saddam213]

Thanks for the PR :)