Cards documentation needs to be more robust

[kevinparkerson]

If you look at the SLDS documentation site, there are a lot more configurations of cards on display than we have showing on the LDSR example site:

https://www.lightningdesignsystem.com/components/cards/
https://design-system-react.herokuapp.com/components/cards/

We should add a few more examples to demonstrate that flexibility, and if there are any limitations create issues to add those features to the card component later on.