Update README.md

demos/text_to_speech/README.md

-
-
 # TTS (Text To Speech)
 
 ## Introduction
@@ -18,28 +16,32 @@ Input of this demo should be a text of the specific language that can be passed
 ### 3. Usage
 - Command Line (Recommended)
     - Chinese
+    
+        The default acoustic model is `Fastspeech2`, and the default vocoder is `Parallel WaveGAN`.
         ```bash
         paddlespeech tts --input "你好，欢迎使用百度飞桨深度学习框架！"
         ```
-    The default acoustic model is `Fastspeech2`, and the default vocoder is `Parallel WaveGAN`.
     - Chinese, use `SpeedySpeech` as acoustic model
         ```bash
         paddlespeech tts --am speedyspeech_csmsc --input "你好，欢迎使用百度飞桨深度学习框架！"
         ```
     - Chinese, multi speaker
+    
+        You can change `spk_id` here.
         ```bash
         paddlespeech tts --am fastspeech2_aishell3 --voc pwgan_aishell3 --input "你好，欢迎使用百度飞桨深度学习框架！" --spk_id 0
         ```
-    You can change `spk_id` here.
+    
      - English
         ```bash
         paddlespeech tts --am fastspeech2_ljspeech --voc pwgan_ljspeech --lang en --input "hello world"
         ```
     - English, multi speaker
+    
+        You can change `spk_id` here.
         ```bash
         paddlespeech tts --am fastspeech2_vctk --voc pwgan_vctk --input "hello, boys" --lang en --spk_id 0
         ```   
-    You can change `spk_id` here.
   Usage:
   
   ```bash