Update README.md

Author: sunlubo

README.md

@@ -1,3 +1,58 @@
 # SwiftSDL2
 
-A description of this package.
+A Swift wrapper for the SDL2 API
+
+## Installation
+
+You should install [SDL2](https://www.libsdl.org/) before use this library, on macOS, you can:
+
+```bash
+brew install sdl2
+```
+
+### Swift Package Manager
+
+SwiftSDL2 primarily uses [SwiftPM](https://swift.org/package-manager/) as its build tool, so we recommend using that as well. If you want to depend on SwiftFFmpeg in your own project, it's as simple as adding a `dependencies` clause to your `Package.swift`:
+
+```swift
+dependencies: [
+    .package(url: "https://github.com/sunlubo/SwiftSDL2.git", from: "0.0.1")
+]
+```
+
+## Usage
+
+```swift
+import SwiftSDL2
+import Darwin
+
+try initSDL(flags: [.video, .audio])
+
+let window = Window(title: "hello", width: 640, height: 480, flags: .resizable)
+let renderer = Renderer(window: window)
+let texture = Texture(renderer: renderer, format: .rgba8888, access: .target, width: 640, height: 480)
+
+while true {
+    var event = Event()
+    Events.pollEvent(&event)
+    if event.type == .quit {
+        break
+    }
+
+    let x = arc4random() % 540
+    let y = arc4random() % 430
+    let rect = Rect(x: Int(x), y: Int(y), w: 100, h: 50)
+
+    try renderer.setTarget(texture)
+    try renderer.setDrawColor(Color(r: 0x00, g: 0x00, b: 0x00, a: 0x00))
+    try renderer.clear()
+    try renderer.drawRect(rect)
+    try renderer.setDrawColor(Color(r: 0xFF, g: 0x00, b: 0x00, a: 0x00))
+    try renderer.fillRect(rect)
+    try renderer.setTarget(nil)
+    try renderer.copy(texture: texture, srcRect: nil, dstRect: nil)
+    renderer.present()
+}
+
+quitSDL()
+```