fix: add aspect ratio to signals.mdx example

packages/docs/docs/getting-started/signals.mdx

@@ -167,7 +167,7 @@ We can use the fact that properties of nodes are represented by signals to
 construct scenes that automatically update when the data changes. Following the
 previous example, let's create a visualisation for the area of the circle:
 
-```tsx editor
+```tsx editor ratio=16/9
 import {makeScene2D} from '@motion-canvas/2d/lib/scenes';
 import {Circle, Txt, Line} from '@motion-canvas/2d/lib/components';
 import {createSignal} from '@motion-canvas/core/lib/signals';