docs(models_zh_cn): add print statement to download models example

Add a print statement to the example code in 'how_to_download_models_zh_cn.md' to
output the downloaded model directory path. This enhancement aids users in locating
the model files as it provides a clear indication of where they are saved on the
user's file system.

docs/how_to_download_models_zh_cn.md

@@ -42,6 +42,7 @@ pip install modelscope
 # 使用modelscope sdk下载模型
 from modelscope import snapshot_download
 model_dir = snapshot_download('wanderkid/PDF-Extract-Kit')
+print(f"模型文件下载路径为：{model_dir}")
 ```
 
 ## 额外步骤