Add link to annual media developer survey.

This will be removed after the survey has closed in ~1 month.

PiperOrigin-RevId: 399890121

docs/index.md

 ---
 ---
 layout: article
 layout: article
 ---
 ---
+The Android media team is interested in your experiences with the Android media
+APIs and developer resources. Please provide your feedback by
+[completing this short survey](https://goo.gle/media-survey-6).
+{:.info}
 
 
 ExoPlayer is an application level media player for Android. It provides an
 ExoPlayer is an application level media player for Android. It provides an
 alternative to Android’s MediaPlayer API for playing audio and video both
 alternative to Android’s MediaPlayer API for playing audio and video both