Add initial information to README

Author: dmadison

README.md

@@ -1,5 +1,51 @@
 # Arduino XInput Library
 
+This library lets you easily emulate an Xbox 360 controller using a USB-capable Arduino microcontroller.
+
+## Getting Started
+
+```cpp
+void setup() {
+	XInput.begin();
+}
+
+void loop() {
+	XInput.press(BUTTON_A);
+	delay(1000);
+	
+	XInput.release(BUTTON_A);
+	delay(1000);
+}
+```
+
+Before the library will work, you must install a compatible boards file that contains the XInput USB descriptors, otherwise the microcontroller won't behave like an XInput device. **This is not optional**. See the [compatible boards](#compatible-boards) section below for more information.
+
+After installing a compatible boards package, you must then [download and install the library](https://www.arduino.cc/en/guide/libraries). Once the XInput library is installed, open up the Arduino IDE and load an example sketch, located in `File -> Examples -> XInput` (I suggest trying the 'Blink' sketch first). Double-check that you have the correct XInput board selected in the 'Tools' menu, then upload the sketch to your microcontroller.
+
+On Windows, you can test that the sketch is working properly by opening up the joystick control panel ([joy.cpl](https://support.microsoft.com/en-us/help/831361/how-to-troubleshoot-game-controllers-in-microsoft-games)) or by using [GamepadViewer.com](https://gamepadviewer.com/?p=1). If you uploaded the XInput 'Blink' example, the #1 button ('A') should be slowly turning on and off.
+
+## Control Surfaces
+
+The library gives you access to the following controls available on the Xbox 360 controller:
+* 10 + 1 Digital Buttons
+* 2 Analog Joysticks (16 bit)
+* 2 Analog Triggers (8 bit)
+* 1 Four-Way Directional Pad (D-Pad)
+
+The library also processes received data, so you can read the status of the controller's 2 rumble motors (8-bit), the assigned player number (1-4), and the index of the current LED animation. Data is sent and received automatically over USB.
+
+## Compatible Boards
+
+To function as an XInput device, you *must* use a compatible boards package with XInput USB descriptors. **This is not optional**. Without these descriptors the library will only function in "debug" mode and the microcontroller will not behave as an XInput device.
+
+The following boards packages are available:
+
+* #### [Arduino AVR Boards](https://www.github.com/dmadison/ArduinoXInput_AVR)
+  Modifies the Arduino AVR core to emulate an XInput device. Includes support for the Arduino Leonardo, Micro, Yun, and more. 
+
+* #### [Teensy 3 Boards](https://www.github.com/dmadison/ArduinoXInput_Teensy)
+  Includes an 'XInput' USB mode for the Teensy 3.1, 3.2, 3.5, 3.6, and LC microcontrollers. Requires a preexisting Teensyduino installation.
+
 ## License
 
 This library is licensed under the terms of the [MIT license](https://opensource.org/licenses/MIT). See the [LICENSE](LICENSE) file for more information.