如何在Magento中创建一个简单的"Hello World"模块？

<?xml version="1.0"?><config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
   <module name="VendorName_HelloWorld" setup_version="1.0.0">
       <sequence>
           <module name="Magento_Store"/>
        </sequence>
    </module>
</config>

<?php
namespace VendorName\HelloWorld\Controller;

use Magento\Framework\App\Action\Context;
use Magento\Framework\View\Result\PageFactory;

class Index extends \Magento\Framework\App\Action
{
    protected $_pageFactory;

    public function __construct(Context $context, PageFactory $pageFactory)
    {
        $this->_pageFactory = $pageFactory;
        parent::__construct($context);
    }

    public function execute()
    {
        echo "Hello World!";
    }
}

<?xml version="1.0"?><config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:App/etc/routes.xsd">
   <router id="standard">
       <route id="helloworld" frontName="helloworld">
           <module name="VendorName_HelloWorld"/>
        </route>
    </router>
</config>