added a npm package to the `built with` section in README.md
added a npm package to the `built with` section in README.md

Responsive grid components for styled-components. https://github.com/jameslnewell/styled-components-grid
JamieDixon/styled-components,JamieDixon/styled-components,styled-components/styled-components,styled-components/styled-components,css-components/styled-components,styled-components/styled-components,JamieDixon/styled-components