Update ReadMe and removed the unnecessary comment

Author: ajaswal

README.md

@@ -94,8 +94,8 @@ thumbImage            | [source](http://facebook.github.io/react-native/docs/ima
 debugTouchArea        | bool     | Yes      | false                     | Set this to true to visually see the thumb touch rect in green.
 animateTransitions    | bool     | Yes      | false                     | Set to true if you want to use the default 'spring' animation
 animationType         | string   | Yes      | 'timing'                  | Set to 'spring' or 'timing' to use one of those two types of animations with the default [animation properties](https://facebook.github.io/react-native/docs/animations.html).
-animationConfig       | object   | Yes      | undefined                 | Used to configure the animation parameters.  These are the same parameters in the [Animated library](https://facebook.github.io/react-native/docs/animations.html). 
-
+animationConfig       | object   | Yes      | undefined                 | Used to configure the animation parameters.  These are the same parameters in the [Animated library](https://facebook.github.io/react-native/docs/animations.html).
+trackClickable        | bool     | Yes      | false                     | Set to true to update the value whilst clicking the Slider
 
 ---
 

src/Slider.js

@@ -321,7 +321,6 @@ export default class Slider extends PureComponent {
   };
 
   _handlePanResponderGrant = (e: Object, gestureState: Object) => {
-    // this._previousLeft = this._getThumbLeft(this._getCurrentValue());
     this._previousLeft = this.props.trackClickable ? gestureState.x0 - (this.state.thumbSize.width/2) : this._getThumbLeft(this._getCurrentValue());
     this._fireChangeEvent('onSlidingStart');
   };