Update the responsive docs about resizing the parent node (#5974)

Add a note about resizing the chart height with maintainAspectRatio

Author: janelledement

docs/general/responsive.md

@@ -33,8 +33,11 @@ The chart can also be programmatically resized by modifying the container size:
 
 ```javascript
 chart.canvas.parentNode.style.height = '128px';
+chart.canvas.parentNode.style.width = '128px';
 ```
 
+Note that in order for the above code to correctly resize the chart height, the [`maintainAspectRatio`](#configuration-options) option must also be set to `false`.
+
 ## Printing Resizeable Charts
 
 CSS media queries allow changing styles when printing a page. The CSS applied from these media queries may cause charts to need to resize. However, the resize won't happen automatically. To support resizing charts when printing, one needs to hook the [onbeforeprint](https://developer.mozilla.org/en-US/docs/Web/API/WindowEventHandlers/onbeforeprint) event and manually trigger resizing of each chart.