docs(readme): add npm badge

README.md

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 # Ray – WeWork Design System
 
-[![Netlify Status](https://api.netlify.com/api/v1/badges/1fc61cc7-d0e8-4424-977e-8fa3f3a237b2/deploy-status)](https://app.netlify.com/sites/ray-docs/deploys) [![CircleCI](https://circleci.com/gh/wework/ray.svg?style=svg)](https://circleci.com/gh/wework/ray) [![Commitizen friendly](https://img.shields.io/badge/commitizen-friendly-brightgreen.svg)](http://commitizen.github.io/cz-cli/) [![Coverage Status](https://coveralls.io/repos/github/wework/ray/badge.svg?branch=master)](https://coveralls.io/github/wework/ray?branch=master)
+[![Netlify Status](https://api.netlify.com/api/v1/badges/1fc61cc7-d0e8-4424-977e-8fa3f3a237b2/deploy-status)](https://app.netlify.com/sites/ray-docs/deploys) [![CircleCI](https://circleci.com/gh/wework/ray.svg?style=svg)](https://circleci.com/gh/wework/ray) [![Commitizen friendly](https://img.shields.io/badge/commitizen-friendly-brightgreen.svg)](http://commitizen.github.io/cz-cli/) [![Coverage Status](https://coveralls.io/repos/github/wework/ray/badge.svg?branch=master)](https://coveralls.io/github/wework/ray?branch=master) [![NPM Version](https://img.shields.io/npm/v/@wework/ray-core.svg)](https://www.npmjs.com/package/@wework/ray-core)
 
 <page-intro>Resources for building interfaces with WeWork's design system. [npm package](https://www.npmjs.com/package/@wework/ray-core)</page-intro>