fixed whitespace

main.py

@@ -339,7 +339,7 @@ async def index_page(client: Client) -> None:
             example_link('Lightbox', 'A thumbnail gallery where each image can be clicked to enlarge')
             example_link('ROS2', 'Using NiceGUI as web interface for a ROS2 robot')
             example_link('Docker Image',
-                         'Demonstrate using the official'
+                         'Demonstrate using the official '
                          '[zauberzeug/nicegui](https://hub.docker.com/r/zauberzeug/nicegui) docker image')
             example_link('Download Text as File', 'providing in-memory data like strings as file download')