Added note for installing React. (#2369)

Author: awhitford

apps/docs/content/docs/frameworks/astro.mdx

@@ -19,7 +19,13 @@ To use NextUI in your Astro project, you need to follow the following steps:
 
 <Steps>
 
-### Installation
+### Install React
+
+NextUI is built on top of React, so you need to install React first. You can follow the official
+[integration guide](https://docs.astro.build/en/guides/integrations-guide/react/) to install React.
+
+
+### Install NextUI
 
 In your Astro project, run one of the following command to install NextUI: