Update README.md

demos/text_to_speech/README.md

@@ -40,9 +40,9 @@ Input of this demo should be a text of the specific language that can be passed
     	```
      You can change `spk_id` here.
 	   
+  Usage:
   
-- Usage:
-```bash
+  ```bash
   paddlespeech tts --help
   ```
   Arguments: