docs(starters): add styled-components starter (#12130)
docs(starters): add styled-components starter (#12130)

## Description

Modified the default starter to use styled components allowing for a basic way to get up and running with Gatsby and styled components. 



gatsbyjs/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby