Add prepare script

Based on https://stackoverflow.com/questions/40528053/npm-install-and-build-of-forked-github-repo

Author: Joel Poloney

package.json

@@ -13,6 +13,7 @@
     "umd"
   ],
   "scripts": {
+    "prepare": "nwb build-react-component",
     "build": "nwb build-react-component",
     "deploy": "gh-pages -d demo/dist",
     "clean": "nwb clean-module && nwb clean-demo",