Add EPA customer story to cloud.gov homepage

[markdboyd]

Background

We have an FEC case study highlighted on the homepage: https://cloud.gov/

We should figure out how to also highlight the EPA case study that we wrote on our homepage: https://cloud.gov/docs/customer-stories/epa-airnow-gov/

Options

Maybe we could make the box for the FEC case study half as wide and put the EPA story beside it?

We'll have to experiment and see what looks best

Acceptance criteria

• Link to EPA customer story for the homepage