HTML directory in config

Hello,

in the documentation the HTML config parameter is described as the "Path to the HTML file generated by the Swagger document generator"

But in the actual implementation it just returns the string set in the config and is not looking for the file to return.
Also setting the parameter "html" does not save the generated html inside of the configured file.

From HttpServer:
#https://github.com/hyperf/swagger/blob/master/src/HttpServer.php#L100

```php
protected function getHtml(): string
{
if (! empty($this->config['html'])) {
return $this->config['html'];
}

return <<<'HTML'
...
HTML;
}
```

Do i miss something or is this just not correctly implemented yet?

Thanks and kind regards