luojianingfix: add beta notes in markdown

Configuring Dark Mode

Note:

Currently in the beta phase.

The Web component supports dark mode configuration for frontend pages.

The darkMode() interface can be used to configure different dark modes, which is disabled by default. When dark mode is enabled, the Web component will apply the dark styles defined in the webpage's media query prefers-color-scheme. If the webpage doesn't define dark styles, it will remain unchanged. To enable forced dark mode, it is recommended to use it in conjunction with forceDarkAccess(). The WebDarkMode.Off mode indicates that dark mode is disabled. WebDarkMode.On indicates that dark mode is enabled and follows the frontend page's settings. WebDarkMode.Auto indicates that dark mode is enabled and follows the system settings.

In the following example, the darkMode() interface is used to configure the page's dark mode to follow the system settings.
```
// index.cj
import ohos.web.webview.WebviewController
import kit.ArkUI.{Web, WebDarkMode}
import ohos.arkui.state_macro_manage.rawfile

@Entry
@Component
class EntryView {
    let webController = WebviewController()

    func build() {
        Column {
            Web(src: @rawfile("index.html"), controller: webController)
                .darkMode(WebDarkMode.Auto)
        }
    }
}
```

The forceDarkAccess() interface can be used to forcibly configure the frontend page to dark mode. Forced dark mode cannot guarantee that all color conversions will meet expectations, and the dark mode will not follow the frontend page or system settings. When configuring this mode, the dark mode must be set to WebDarkMode.On.

In the following example, the forceDarkAccess() interface is used to forcibly configure the page to dark mode.

// index.cj
import ohos.web.webview.WebviewController
import kit.ArkUI.{Web, WebDarkMode}
import ohos.arkui.state_macro_manage.rawfile

@Entry
@Component
class EntryView {
    let webController = WebviewController()

    func build() {
        Column {
            Web(src: @rawfile("index.html"), controller: webController)
                .darkMode(WebDarkMode.On)
                .forceDarkAccess(true)
        }
    }
}

index.html page code:

<!-- resources/rawfile/index.html -->
<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width,
                                    initial-scale=1.0,
                                    maximum-scale=1.0,
                                    user-scalable=no">
    <style type="text/css">
        @media (prefers-color-scheme: dark) {
            .contentCss{ background:  #000000; color: white; }
            .hrefCss{ color: #317AF7; }
        }
    </style>
</head>
<body class="contentCss">
<div style="text-align:center">
    <p>Dark mode debug page</p>
</div>
</body>
</html>