📝 Update README

README.md

@@ -1,4 +1,104 @@
 # SoundIO
-A Swift wrapper for libsoundio.
 
 ![Github Status](https://github.com/thara/SoundIO/workflows/Swift/badge.svg)
+
+A Swift wrapper for [libsoundio](https://github.com/andrewrk/libsoundio), a cross-platform real-time audio input and output library.
+
+## Requirements
+
+- libsoundio
+
+## Installation
+
+```swift
+    dependencies: [
+        .package(url: "https://github.com/thara/SoundIO.git", from: "0.1.0"),
+    ]
+```
+
+## Example
+
+The following emits a sine wave over the default device using the best backend.   
+It means as same as [libsoundio's synopsis](https://github.com/andrewrk/libsoundio#synopsis).
+
+```swift
+import Foundation
+import SoundIO
+
+var secondsOffset: Float = 0.0
+
+func main() throws {
+    let soundio = try SoundIO()
+    try soundio.connect()
+    soundio.flushEvents()
+
+    let outputDeviceIndex = try soundio.defaultOutputDeviceIndex()
+    let device = try soundio.getOutputDevice(at: outputDeviceIndex)
+    print("Output device: \(device.name)")
+
+    let outstream = try OutStream(to: device)
+    outstream.format = .float32bitLittleEndian
+    outstream.writeCallback { (outstream, frameCountMin, frameCountMax) in
+        let layout = outstream.layout
+        let secondsPerFrame = 1.0 / Float(outstream.sampleRate)
+
+        try! outstream.write(frameCount: frameCountMax) { (areas, frameCount) in
+            let pitch: Float = 440.0
+            let radiansPerSecond = pitch * 2.0 * .pi
+            for frame in 0..<frameCount {
+                let sample = sin((secondsOffset + Float(frame) * secondsPerFrame) * radiansPerSecond)
+                if frame == 100 {
+                    print("\(secondsOffset) \(frame) \(secondsPerFrame) \(radiansPerSecond) \(sample)")
+                }
+                for area in areas.iterate(over: layout.channelCount) {
+                    area.write(sample, stepBy: frame)
+                }
+            }
+            secondsOffset = (secondsOffset + secondsPerFrame * Float(frameCount)).truncatingRemainder(dividingBy: 1)
+        }
+    }
+
+    try outstream.open()
+    try outstream.start()
+
+    while true {
+        soundio.waitEvents()
+    }
+}
+
+do {
+    try main()
+} catch let error as SoundIOError {
+    print("Error: \(error)")
+    exit(EXIT_FAILURE)
+}
+```
+
+This code is located in `Sources/SoundIODemo/main.swift`.
+You can run it by using `make demo`.
+
+### Notes
+
+You haven't need to call any `**_destroy` functions because the wrapper calls each of `**_destroy` functions in `deinit` and destroyed out of scopes properly.
+
+## TODO
+
+- [ ] Add documentation
+- [ ] Support error/underflow callbacks in `OutStream`
+- [ ] Implement `InStream`
+- [ ] Add examples
+- [ ] Test other platforms except macOS
+
+## Author
+
+*Tomochika Hara* - [thara](https://github.com/thara)
+
+## License
+
+This project is licensed under the MIT License - see the [LICENSE](./LICENSE) file for details
+
+## Acknowledgments
+
+- [libsoundio](https://github.com/andrewrk/libsoundio)
+- [rsoundio](https://github.com/klingtnet/rsoundio)
+  - This has gaven me an idea to keep callback functions in stream's userdata.