Provide examples of assets needed to generate

I keep running into the same issue when I myself begin a project or anyone else. What should we provide for each asset? What are the differences between the icons? What should they look like? What is the foreground and what is the background? I think it would be very helpful if we provided examples in either documentation or provided a command the generates them.

```
assets/
├── icon-only.png
├── icon-foreground.png
├── icon-background.png
├── splash.png
└── splash-dark.png
```