docs(image): added to the usage docs

src/components/Image/Image.md

@@ -6,6 +6,7 @@
 * You can use the `contentful API` to request an image of a certain size.
 * `rounded="circle"` requires a square image `(width == height)` in order to generate a perfect circle.
 * Non-square images will give a warning and will appear oval shaped.
+* When using the image symbol in the Sketch file, replace the image in the overrides with and image with the same aspect ratio.
 
 ```jsx
 <Image src="image-example.jpg" rounded="corners" width={300} height={300} alt="Image of co-workers collaborating" />