Add SwiftUI documentation

[bryankeller]

Details

This PR adds SwiftUI documentation, some organization tweaks, and some updated tutorial screenshots to the README.md. Previously, there was only a tutorial for UIKit. Now, each section of the tutorial has a SwiftUI and UIKit collapsable section that can be expanded.

Related Issue

N/A

Motivation and Context

Docs are good

How Has This Been Tested

N/A

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.