document node requirements

Author: mbostock

docs/index.html

@@ -17,13 +17,15 @@
     ```bash
     npm install @observablehq/notebook-kit
     ```
+
+    Notebook Kit requires [Node.js](https://nodejs.org/en) 20.19+ or 22.12+.
   </script>
   <script id="8" type="text/markdown">
     ---
 
     ## Command-line interface
 
-    Notebook Kit's CLI supports three commands: `preview` for a live preview of notebooks, `build` for building a static site, and `download` for downloading a notebook from Observable as HTML. The `preview` and `build` commands are powered by [Vite](https://vite.dev).
+    Notebook Kit's CLI supports three commands: `preview` for a live preview of notebooks, `build` for building a static site, and `download` for downloading Observable Notebooks as HTML.
   </script>
   <script id="9" type="text/markdown">
     ### Preview