create readme

Author: elringus

README.md

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+## Download package
+For Unity 2017.4 and later: [UnityRawInput.unitypackage](https://github.com/Elringus/UnityRawInput/releases/download/v1.0/UnityRawInput.unitypackage).
+
+## Description
+Wrapper over [Windows Raw Input API](https://msdn.microsoft.com/en-us/library/windows/desktop/ms645536(v=vs.85).aspx) to hook for the native input events.
+Allows to receive input events even when the Unity application is in background (not in focus).
+Will only work on Windows platform.
+
+## Usage
+Include package namespace.
+```csharp
+using UnityRawInput;
+```
+Initialize the input service to start processing native input messages. 
+```csharp
+RawKeyInput.Start();
+```
+Optinally, you can specify whether input messages should be handled when the application is not in focus (disabled by default).
+```csharp
+var workInBackground = true;
+RawKeyInput.Start(workInBackground);
+```
+Add listeners for the input events.
+```csharp
+RawKeyInput.OnKeyUp += HandleKeyUp;
+RawKeyInput.OnKeyDown += HandleKeyDown;
+
+private void HandleKeyUp (RawKey key) { ... }
+private void HandleKeyDown (RawKey key) { ... }
+```
+You can also check whether specific key is currently pressed.
+```csharp
+if (RawKeyInput.IsKeyDown(key)) { ... }
+```
+You can stop the service at any time.
+```csharp
+RawKeyInput.Stop();
+```
+Don't forget to remove listeners when you no longer need them.
+```csharp
+private void OnDisable ()
+{
+    RawKeyInput.OnKeyUp -= HandleKeyUp;
+    RawKeyInput.OnKeyDown -= HandleKeyDown;
+}
+```