Add screenshot of button device classes (#20553)

source/_integrations/button.markdown

@@ -58,6 +58,11 @@ This service can be called to trigger a button press for that entity.
 The way these buttons are displayed in the frontend can be modified in the [customize section](/docs/configuration/customizing-devices/).
 The following device classes are supported for buttons:
 
+<p class='img'>
+<img src='/images/screenshots/button_classes_icons.png' />
+Example of device class icons.
+</p>
+
 - **None**: Generic button. This is the default and doesn't need to be set.
 - **restart**: The button restarts the device.
 - **update**: The button updates the software of the device.