add lockToPortraitUpsideDown() to README

Author: Wonday

Diff for: README.md

@@ -218,6 +218,7 @@ It can return either `PORTRAIT` `LANDSCAPE-LEFT` `LANDSCAPE-RIGHT` `UNKNOWN`
 - `lockToLandscape()`
 - `lockToLandscapeLeft()`  this will lock to camera left home button right
 - `lockToLandscapeRight()` this will lock to camera right home button left
+- `lockToPortraitUpsideDown` only support android
 - `unlockAllOrientations()`
 - `getOrientation(function(orientation))`
 - `getDeviceOrientation(function(deviceOrientation))`

Diff for: index.d.ts

@@ -19,6 +19,7 @@ declare class Orientation {
   static lockToLandscape(): void;
   static lockToLandscapeLeft(): void;
   static lockToLandscapeRight(): void;
+  static lockToPortraitUpsideDown(): void;
   static unlockAllOrientations(): void;
   static getOrientation(callback: (orientation: OrientationType) => void): void;
   static getDeviceOrientation(callback: (orientation: OrientationType) => void): void;