add segment for API reference

www/reference/package.json

@@ -29,6 +29,7 @@
     "gatsby-plugin-preact": "^5.9.0",
     "gatsby-plugin-react-helmet": "^3.3.12",
     "gatsby-plugin-sitemap": "^5.15.0",
+    "gatsby-plugin-segment-js": "^3.7.1",
     "gatsby-plugin-theme-ui": "^0.10.1",
     "gatsby-remark-autolink-headers": "^4.6.0",
     "gatsby-source-filesystem": "^3.9.0",