add api fee notice

app.py

@@ -375,7 +375,7 @@ The grading results will be downloaded as a zip file.
 
 with gr.Blocks() as demo:
     gr.Markdown(markdown)
-    key = gr.Textbox(label="Enter your OpenAI API Key (this space will not save your API Key)", type="password")
+    key = gr.Textbox(label=f"Enter your OpenAI API Key (this space will not save your API Key). [Pay Attention]: this evaluaiton may cost several dollars, please notice your OpenAI API Key balance.", type="password")
     model = gr.Dropdown(
         choices=["gpt-4-0613", "gpt-4-turbo"],
         value="gpt-4-0613",