Added update method docs

Author: pavle-goloskokovic

v3/src/sound/BaseSound.js

@@ -341,7 +341,13 @@ var BaseSound = new Class({
         this.currentConfig.delay = 0;
     },
     /**
+     * Update method called automatically by sound manager on every game step.
+     *
+     * @override
      * @protected
+     * @method Phaser.Sound.BaseSound#update
+     * @param {number} time - The current timestamp as generated by the Request Animation Frame or SetTimeout.
+     * @param {number} delta - The delta time elapsed since the last frame.
      */
     update: NOOP,
     /**