Add a code sample to the readme

Author: mdiep

README.md

@@ -1,9 +1,43 @@
 # ReactiveTask
-
 ReactiveTask is a Swift framework for launching shell tasks (processes), built using [ReactiveCocoa](https://github.com/ReactiveCocoa/ReactiveCocoa).
 
+```swift
+let strings = [ "foo\n", "bar\n", "buzz\n", "fuzz\n" ]
+let input = SignalProducer<NSData, NoError>(values: strings.map { $0.dataUsingEncoding(NSUTF8StringEncoding)! })
+let task = Task("/usr/bin/sort")
+
+// Run the task, ignoring the output, and do something with the final result.
+let result: Result<String, TaskError>? = launchTask(task, standardInput: input)
+    .ignoreTaskData()
+    .map { String(data: $0, encoding: NSUTF8StringEncoding) }
+    .ignoreNil()
+    .single()
+print("Output of `\(task)`: \(result?.value ?? "")")
+
+// Start the task and print all the events, which includes all the output
+// that was received.
+launchTask(task, standardInput: input)
+    .flatMapTaskEvents(.Concat) { data in
+        return SignalProducer(value: String(data: data, encoding: NSUTF8StringEncoding))
+    }
+    .startWithNext { (event: TaskEvent) in
+        switch event {
+        case let .Launch(task):
+            print("launched task: \(task)")
+
+        case let .StandardError(data):
+            print("stderr: \(data)")
+
+        case let .StandardOutput(data):
+            print("stdout: \(data)")
+
+        case let .Success(string):
+            print("value: \(string)")
+        }
+    }
+```
+
 For examples of how to use ReactiveTask, see the Xcode and Git integration code from the [CarthageKit](https://github.com/Carthage/Carthage) framework.
 
 ## License
-
 ReactiveTask is released under the [MIT license](LICENSE.md).