[DOC] Refine Readme

Signed-off-by: LocoRichard <lichen.wang@zilliz.com>

README.md

@@ -10,8 +10,6 @@
 **Audio** **Decode** converts the encoded audio back to uncompressed audio frames. In most cases, audio decoding is the first step of an audio processing pipeline.
 
 
-Using the default audio_decode implementation and writing the pipeline in the simplified way
-
 
 
 <br />
@@ -37,9 +35,9 @@ towhee.glob('./music.mp3').audio_decode().flatten().show(limit=1)
 ### Factory Constructor
 
 
-Create the operator via the following factory method
+Create the operator via the following factory method:
 
-audio_decode.ffmpeg()
+***audio_decode.ffmpeg()***