Add link to primerize docs for primer/react (#903)

* Add link to primerize docs for primer/react

* Update content/guides/react/index.mdx

Co-authored-by: Leslie Cohn-Wein <lesliecdubs@github.com>

---------

Co-authored-by: Leslie Cohn-Wein <lesliecdubs@github.com>

content/guides/react/index.mdx

@@ -4,6 +4,10 @@ description: Get started using Primer React components in your React application
 source: https://github.com/primer/react
 ---
 
+## Dotcom Codespaces (staff-only)
+
+Are you a GitHub employee (Hubber) looking to make a change to primer/react or another Primer library? Take a look at our documentation for the [`primerize` tool](https://github.com/github/primer-engineering/blob/main/how-we-work/developing-in-dotcom-codespaces.md) (GitHub staff only), which can help get you started in a dotcom codespace.
+
 ## Getting started
 
 1. Install `@primer/react` and its peer dependencies: