Add SPI badge and documentation link

Author: Kyle-Ye

README.md

@@ -1,5 +1,7 @@
 # OpenAsyncImage
 
+[![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2FOpenSwiftUIProject%2FOpenAsyncImage%2Fbadge%3Ftype%3Dswift-versions)](https://swiftpackageindex.com/OpenSwiftUIProject/OpenAsyncImage) [![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2FOpenSwiftUIProject%2FOpenAsyncImage%2Fbadge%3Ftype%3Dplatforms)](https://swiftpackageindex.com/OpenSwiftUIProject/OpenAsyncImage)
+
 A backport implementation of SwiftUI's AsyncImage on Apple platform.
 
 ## Overview
@@ -58,6 +60,10 @@ struct ContentView: View {
 }
 ```
 
+## Documentation
+
+Detailed documentation for OpenAsyncImage can be found on [Swift Package Index](https://swiftpackageindex.com/OpenSwiftUIProject/OpenAsyncImage/main/documentation/openasyncimage).
+
 ## Advantages
 
 - **iOS 13+ Support**: Brings AsyncImage functionality to earlier iOS versions instead of being limited to iOS 15+