Update README.

README.md

@@ -32,6 +32,7 @@ import Unswitch from 'unswitch';
 
 // Create the listener
 const unswitch = new Unswitch({
+  side: 'L', // or R
   b: (pressed) => {},
   a: (pressed) => {},
   y: (pressed) => {},
@@ -50,7 +51,7 @@ function render() {
 render();
 ```
 
-Calling `unswitch.update()` will check every button for a change in state. If a callback is provided the new state is passed along. The axis works in the same way, but instead of a `boolean` it will return a `number` from 0 to 8. Number 0 to 7 are for the joystick positions going clockwise, number 8 is used as default (center).
+It's possible to connect up to two controllers at the same time. To make this work `side` is to be passed with either `L` (left) or `R` (right) for the controllers respectively. Calling `unswitch.update()` will check every button for a change in state. If a callback is provided the new state is passed along. The axis works in the same way, but instead of a `boolean` it will return a `number` from 0 to 8. Number 0 to 7 are for the joystick positions going clockwise, number 8 is used as default (center).
 
 > Buttons are mapped based on a single controller positioned horizontally.