Looking at the Gatsby docs, they suggest that you can reference background images like you would anywhere else: 

```
.image {
  background-image: url(./image.png);
}

```

What they don't cover is where these images should live. I've tried placing the image directory in the src folder, in the layout folder, and in the root folder, but I keep getting the error: 

```
Loader /Users/username/Sites/my-app/node_modules/url/url.js?{"limit":10000,"name":"static/[name].[hash:8].[ext]"} didn't return a function
 @ ./~/css-loader!./~/postcss-loader!./src/layouts/index.css 6:400-435

```

What's the proper way to reference a background image using Gatsby?

Current directory structure:

```
my-app
- src
-- images 
--- image.png
-- layouts
--- index.css

```