iOS11 NSPhotoLibraryAddUsageDesc

This app has crashed because it attempted to access privacy-sensitive data without a usage description. The app's Info.plist must contain an NSPhotoLibraryAddUsageDescription key with a string value explaining to the user how the app uses this data.

iOS11以前：
NSPhotoLibraryUsageDescription：访问相册和存储照片到相册（读写），会出现用户授权。

iOS11之后：
NSPhotoLibraryUsageDescription：无需添加。默认开启访问相册权限（读），无需用户授权。
NSPhotoLibraryAddUsageDescription： 添加内容到相册。（写），会出现用户授权。