Mention playerStateStream in the state model section.

just_audio/README.md

@@ -222,6 +222,8 @@ This state model provides a flexible way to capture different combinations of st
 * When buffering occurs during playback (e.g. due to a slow network connection), the app's play/pause button remains in the `playing` state, although temporarily no sound will be audible while `processingState == buffering`. Sound will be audible again as soon as the buffers are filled again and `processingState == ready`.
 * When playback reaches the end of the audio stream, the player remains in the `playing` state with the seek bar positioned at the end of the track. No sound will be audible until the app seeks to an earlier point in the stream. Some apps may choose to display a "replay" button in place of the play/pause button at this point, which calls `seek(Duration.zero)`. When clicked, playback will automatically continue from the seek point (because it was never paused in the first place). Other apps may instead wish to listen for the `processingState == completed` event and programmatically pause and rewind the audio at that point.
 
+Apps that wish to react to both orthogonal states through a single combined stream may listen to `playerStateStream`. This stream will emit events that contain the latest value of both `playing` and `processingState`.
+
 ## Configuring the audio session
 
 If your app uses audio, you should tell the operating system what kind of usage scenario your app has and how your app will interact with other audio apps on the device. Different audio apps often have unique requirements. For example, when a navigator app speaks driving instructions, a music player should duck its audio while a podcast player should pause its audio. Depending on which one of these three apps you are building, you will need to configure your app's audio settings and callbacks to appropriately handle these interactions.