docs(q-a): add how to save video/image to camera roll

docs/QA.md

@@ -4,6 +4,7 @@
 - [Manifest merger failed](#when-i-try-to-build-my-project-i-get-following-error)
 - [How can I resize captured images?](#how-can-i-resize-captured-images)
 - [How can I get thumbnails for my video?](#how-can-i-get-thumbnails-for-my-video)
+- [How can I save my video/image to the camera roll?](#hoc-can-i-save-my-video-image-to-the-camera-roll)
 
 #### meta-data android 26
 
@@ -140,3 +141,9 @@ class CameraComponent extends Component {
 #### How can I get thumbnails for my video
 
 We recommend using the library [`react-native-thumbnail`](https://github.com/phuochau/react-native-thumbnail) for generating thumbnails of your video files.
+
+#### How can I save my video/image to the camera roll?
+
+You can use the [`CameraRoll` Module](https://facebook.github.io/react-native/docs/cameraroll.htm).
+You must follow the setup instructions in the `react-native` documentation, since `CameraRoll` module needs to be linked first.
+