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

Utility function for using breakpoints with `styled-components`. https://github.com/jameslnewell/styled-components-breakpoint
JamieDixon/styled-components,styled-components/styled-components,JamieDixon/styled-components,styled-components/styled-components,css-components/styled-components,JamieDixon/styled-components,styled-components/styled-components