update pubspec description

pubspec.yaml

@@ -1,5 +1,5 @@
 name: flutter_ffmpeg
-description: FFmpeg plugin for Flutter.
+description: Flutter plugin to run FFmpeg in the mobile platform. Supports iOS and Android.
 version: 0.1.0
 author: Taner Sener <tanersener@gmail.com>
 homepage: https://github.com/tanersener/flutter-ffmpeg