docs: add engines documentation

Author: geoffrich

README.md

@@ -43,6 +43,16 @@ If you use a custom API directory (see [below](#apiDir)), your `api_location` wi
 
 If your `app_location` is in a subfolder (e.g. `./my_app_location`), then your `api_location` should include the path to that subfolder (e.g. `my_app_location/build/server`.) `output_location` should still be `build/static`.
 
+### Building with the correct version of Node
+
+Oryx, Azure's build system, may attempt to build your application with an EOL version of Node that SvelteKit doesn't support. If you get an error like "Unsupported engine - Not compatible with your version of node/npm", you can force Oryx to use the correct version by setting an `engines` field in your app's `package.json`:
+
+```js
+"engines": {
+	"node": ">=18.13 <19"
+}
+```
+
 ## Running locally with the Azure SWA CLI
 
 You can debug using the [Azure Static Web Apps CLI](https://github.com/Azure/static-web-apps-cli). Note that the CLI is currently in preview and you may encounter issues.