refactor(readme): add instance methods for datepicker readme

Author: feyy

README.md

@@ -61,10 +61,11 @@ You can check [index.js](https://github.com/xgfe/react-native-datepicker/blob/ma
 | customStyles | - | `number` | The hook of customize datepicker style, same as the native style. `dateTouchBody`, `dateInput`...|
 | showIcon | true | `boolean` | Controller whether or not show the icon |
 | placeholder | '' | `string` | The placeholder show when this.props.date is falsy |
+| onDateChange | - | `function` | This is called when the user confirm the picked date or time in the UI. The first and only argument is a date or time string representing the new date and time formatted by [moment.js](http://momentjs.com/) with the given format property. |
 
-## Methods
-
+## Instance Methods
 
 | Method  | Params  | Description |
 | :------------ |:---------------:| :---------------:|
-| onDateChange | dateStr:string, date:date | This is called when the user confirm the picked date or time in the UI. The first and only argument is a date or time string representing the new date and time formatted by [moment.js](http://momentjs.com/) with the given format property. |
+| onPressDate | - | Manually open the date picker panel |
+| onPressCancel | - | Manually close the date picker panel like, similarly pressing cancel btn |