Use react-datepicker in "fallback" example instead of optgroups

Author: jakeboone02

docs/intro.mdx

@@ -8,22 +8,16 @@ import { SandpackRQB } from '../src/components/SandpackRQB';
 To install `react-querybuilder`, use [npm](https://www.npmjs.com/package/react-querybuilder) or [Yarn](https://yarnpkg.com/package/react-querybuilder).
 
 ```bash
-# npm
 npm i react-querybuilder
-```
-
-or
-
-```bash
-# Yarn
+# OR
 yarn add react-querybuilder
 ```
 
 ## Basics
 
 The simplest way to create a query builder is to render the `QueryBuilder` component with no props. (Be sure to import the official stylesheet, which is available in `.css` and `.scss` flavors.)
 
-<SandpackRQB>
+<SandpackRQB options={{ editorHeight: 160 }}>
 
 ```tsx
 import QueryBuilder from 'react-querybuilder';
@@ -34,11 +28,11 @@ export default () => <QueryBuilder />;
 
 </SandpackRQB>
 
-Functional, but not really useful. To really get value out of the query builder, we'll first need to define a set of fields for the user to choose from. We can pass the `fields` array into the query builder through the `fields` prop.
+Functional, but not very useful. To really get value out of the query builder, we'll first need to define a set of fields for the user to choose from. We can pass the `fields` array into the query builder through the `fields` prop.
 
 In the query builder below, click the "+Rule" button and then the fields selector to see the field choices.
 
-<SandpackRQB>
+<SandpackRQB options={{ editorHeight: 240 }}>
 
 ```tsx
 import QueryBuilder from 'react-querybuilder';
@@ -58,7 +52,7 @@ Much more useful, but you probably want to monitor and control what users do wit
 
 The state variable `query` will be passed to the `query` prop, and the setter method `setQuery` will be used in the `onQueryChange` callback. Let's also seed the query object with a couple of rules, making sure that the `field` property of each rule matches the `name` property of one of our fields.
 
-<SandpackRQB>
+<SandpackRQB options={{ editorHeight: 480 }}>
 
 ```tsx
 import { useState } from 'react';