update the stage of run.sh and synthesize_e2e.sh, to be clear (#4057)

* run.sh修改：为 synthesize 和 synthesize_e2e 添加 --stage 参数控制 vocoder 模型选择，REAMDE.md修改：补充 stage 参数说明，明确 vocoder 选择逻辑

* 添加run.sh中stage参数相关的注释

* HiFiGAN改为MultiBand MelGAN

* cmsc文件改回原位（No.15不修改），这里只对No.6做修改

* update the stage of run.sh and synthesize_e2e.sh, to be clear

* fix the md

examples/aishell3/ernie_sat/README.md

@@ -138,7 +138,7 @@ You can check the text of downloaded wavs in `source/README.md`.
 ```bash
 ./run.sh --stage 3 --stop-stage 3 --gpus 0
 ```
-`stage 3` of `run.sh` calls `local/synthesize_e2e.sh`, `stage 0` of it is **Speech Synthesis** and  `stage 1` of it is **Speech Editing**.
+`stage 3` of `run.sh` calls `local/synthesize_e2e.sh`. `synthesize_e2e.sh` is a script for performing both **Speech Synthesis** and **Speech Editing** tasks by default. It converts input text into speech for synthesis and modifies existing speech based on new text content for editing.
 
 You can modify `--wav_path`、`--old_str` and `--new_str` yourself, `--old_str`  should be the text corresponding to the audio of  `--wav_path`, `--new_str` should be designed according to `--task_name`, both `--source_lang` and `--target_lang` should be `zh` for model trained with AISHELL3 dataset.
 ## Pretrained Model