[Website] post-v2 Content item nesting

[RichKummer]

We held off on including nesting info for content item, but a useful future enhancement would include using content item in groups. Storybook is useful for seeing one content item in action – we also discussed having Storybook options for nesting content item inside other components. But the website can help guide adopters for laying out content item more:

• Arranging in a horizontal row
• Arranging vertical content items in one to a row
• Arranging vertical content items two to a row