fix: replace broken GIFs in README by videos

I uploaded the videos via the online editor of GitHub. GitHub provides
drag-and-drop functionality so that one can insert images and videos
directly into READMEs. The uploaded files are stored outside of the
Git repository. For further info, see https://stackoverflow.com/a/4279746.

README.md

@@ -145,7 +145,7 @@ For full usage details refer to the **[Wiki](https://github.com/miguelpruivo/flu
 
 ## Example App
 #### Android
-![DemoAndroid](https://github.com/miguelpruivo/flutter_file_picker/blob/bugfix/%231254-current-directory-changes-after-picking-files/example/screenshots/example_android.gif)
+https://user-images.githubusercontent.com/9049899/231513581-12dbbaa1-5c5d-4c81-9e44-f7cd5207180b.mp4
 
 #### iOS
 ![DemoMultiFilters](https://github.com/miguelpruivo/flutter_file_picker/blob/master/example/screenshots/example_ios.gif)
@@ -154,17 +154,15 @@ For full usage details refer to the **[Wiki](https://github.com/miguelpruivo/flu
 ![DemoMacOS](https://github.com/miguelpruivo/flutter_file_picker/blob/master/example/screenshots/example_macos.png)
 
 #### Linux
-![DemoLinux](https://github.com/miguelpruivo/flutter_file_picker/blob/bugfix/%231254-current-directory-changes-after-picking-files/example/screenshots/example_linux.gif)
+https://user-images.githubusercontent.com/9049899/231513766-90a9cc75-b5c0-4816-ba15-4e3d3e2a6274.mp4
+
 
 #### Windows
-![DemoWindows](https://github.com/miguelpruivo/flutter_file_picker/blob/bugfix/%231254-current-directory-changes-after-picking-files/example/screenshots/example_windows.gif)
+https://user-images.githubusercontent.com/9049899/231513826-958bd1d3-334b-4036-b126-3ff4ca716992.mp4
 
 ## Getting Started
 
 For help getting started with Flutter, view our online
 [documentation](https://flutter.io/).
 
 For help on editing plugin code, view the [documentation](https://flutter.io/platform-plugins/#edit-code).
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