Adds an image of the gui demo

README.md

@@ -531,6 +531,8 @@ Implemented:
 
 `dialog-error`, `dialog-info`, `dialog-open-file`, `dialog-save-file`, `container`, `container-add-to`, `conainer-scroll`, `container-size`, `gui-add-window`, `gui-create`, `gui-list-windows`, `gui-use-light-theme`, `widget-add-to-size`, `widget-get-text`, `widget-hide`, `widget-make-button`, `widget-make-checkbox`, `widget-make-entery`, `widget-make-hyperlink`, `widget-make-image`, `widget-make-label`, `widget-make-markdown`, `widget-make-multiline`, `widget-make-password`, `widget-make-select`, `widget-make-separator`, `widget-make-spacer`, `widget-set-text`, `widget-resize`, `widget-show`, `widget-size`, `window-allow-resize`, `window-center`, `window-close`, `window-hide`, `window-resize`,`window-set-content`, `window-set-fullscreen`, `window-set-title`, `window-show`, `window-show-and-run`
 
+![Demonstration of slope gui](/images/slope-gui-demo.png)
+
 <details>
   <summary>GUI API Description</summary>
   <p>Anything inside `[]` is a placeholder representing an argument. Anything inside `[[]]` is a placeholder representing an _optional_ argument. `...` indicates a variadic value.</p>