`app.py`: add default prompt

app.py

@@ -105,7 +105,7 @@ with gr.Blocks(css=css) as demo:
     with gr.Tab("txt2img"):
         with gr.Row():
             with gr.Column(scale=6, min_width=600):
-                prompt = gr.Textbox(placeholder="Prompt", show_label=False, lines=3)
+                prompt = gr.Textbox("puppies in a cloud, 4k", placeholder="Prompt", show_label=False, lines=3)
                 negative_prompt = gr.Textbox(placeholder="Negative Prompt", show_label=False, lines=3)
             with gr.Column(equal_height=True):
                 text_button = gr.Button("Generate", variant='primary', elem_id="generate")