Update README.md

README.md

@@ -55,6 +55,7 @@ The dataset contains an audiobook chapter level manifest with these fields:
 
 - **url**: Download URL for the LibriVox audiobook chapter
 - **chapter_filepath**: Relative path where audiobook chapter is stored
+- **duration**: Duration of chapter
 - **bandwidth**: Bandwidth estimated using the first 30 seconds of the chapter
 - **utterances**: List of utterance metadata with the following fields
 - **utterances.audio_filepath**: Relative path where utterance is stored