https://www.hackingwithswift.com/100/swiftui/19
- User select input unit
- Enter value
- See output conversion
- Temperature conversion: users choose Celsius, Fahrenheit, or Kelvin.
- Length conversion: users choose meters, kilometers, feet, yards, or miles.
- Time conversion: users choose seconds, minutes, hours, or days.
- Volume conversion: users choose milliliters, liters, cups, pints, or gallons.
