Add volume effect to docs

Author: Jeff Shillitto

README.md

@@ -345,6 +345,7 @@ videoAsset
   .setSrc('https://shotstack-assets.s3.aws.com/mountain.mp4')
   .setTrim(5)
   .setVolume(0.5)
+  .setVolumeEffect('fadeIn')
   .setCrop(crop);
 ```
 
@@ -355,6 +356,7 @@ Method | Description | Required
 setSrc(string url) | The video source URL. The URL must be publicly accessible or include credentials. | Y
 setTrim(float seconds) | The start trim point of the video clip, in seconds (defaults to 0). Videos will start from the in trim point. The video will play until the file ends or the Clip length is reached. | -
 setVolume(float level) | Set the volume for the video clip between 0 and 1 where 0 is muted and 1 is full volume (defaults to 0). | -
+setVolumeEffect(string effect) | The volume effect to apply to the video asset.<ul><li>`fadeIn` - fade volume in only</li><li>`fadeOut` - fade volume out only</li><li>`fadeInFadeOut` - fade volume in and out</li></ul> | -
 setCrop([Shotstack.Crop](#crop) crop) | Crop the sides of an asset by a relative amount. The size of the crop is specified using a scale between 0 and 1, relative to the screen width - i.e. a left crop of 0.5 will crop half of the asset from the left, a top crop of 0.25 will crop the top by quarter of the asset. | -
 
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