Extend documentation for ForwardingPlayer

Add some additional information which methods to override
for available commands.

#minor-release

PiperOrigin-RevId: 513251805
(cherry picked from commit a64a9e6)

docs/customization.md

@@ -225,14 +225,20 @@ the following:
 When overriding `ForwardingPlayer` methods it's important to ensure the
 implementation remains self-consistent and compliant with the `Player`
 interface, especially when dealing with methods that are intended to have
-identical or related behavior. For example, if you want to override every 'play'
-operation, you need to override both `ForwardingPlayer.play` and
-`ForwardingPlayer.setPlayWhenReady`, because a caller will expect the behavior
-of these methdods to be identical when `playWhenReady = true`. Similarly, if you
-want to change the seek-forward increment you need to override both
-`ForwardingPlayer.seekForward` to perform a seek with your customized increment,
-and `ForwardingPlayer.getSeekForwardIncrement` in order to report the correct
-customized increment back to the caller.
+identical or related behavior. For example:
+* If you want to override every 'play' operation, you need to override both
+  `ForwardingPlayer.play` and `ForwardingPlayer.setPlayWhenReady`, because a
+  caller will expect the behavior of these methods to be identical when
+  `playWhenReady = true`.
+* If you want to change the seek-forward increment you need to override both
+  `ForwardingPlayer.seekForward` to perform a seek with your customized
+  increment, and `ForwardingPlayer.getSeekForwardIncrement` in order to report
+  the correct customized increment back to the caller.
+* If you want to control what `Player.Commands` are advertised by a player
+  instance, you must override `Player.getAvailableCommands()`,
+  `Player.isCommandAvailable()` and also listen to the
+  `Player.Listener.onAvailableCommandsChanged()` callback to get notified of
+changes coming from the underlying player.
 
 ## MediaSource customization ##