Add description of environment variables of gradio

gradio.md

@@ -95,3 +95,11 @@ demo.launch(share=True, height=800)
 ```
 
 This will use gradio's service to make a public link tunneling to the gradio server.
+
+## Environment Variables
+
+If you need to set such a parameter, but the script you run is not your code, you can still set these parameters via [environment variables](https://www.gradio.app/guides/environment-variables). For example to start `llamafactory`'s webui, which is built using gradio, with changed parameters:
+
+``` bash
+GRADIO_SERVER_NAME="0.0.0.0" llamafactory-cli webui
+```