Add support for Web App Manifest in siteConfig

docs/api-site-config.md

@@ -147,6 +147,8 @@ h1 {
 * `defaultLang` defines a default language. It will be used if one is not specified at the top of the code block. You can find the [list of supported languages here](https://github.com/isagalaev/highlight.js/tree/master/src/languages).
 * `themeUrl` is the custom URL of CSS theme file that you want to use with Highlight.js. If this is provided, the `theme` and `version` fields will be ignored.
 
+`manifest` - Local path to your Web App Manifest (e.g., `/manifest.json`). This will add manifest.json to head link with rel as "manifest".
+
 `markdownPlugins` - An array of plugins to be loaded by Remarkable, the markdown parser and renderer used by Docusaurus. The plugin will receive a reference to the Remarkable instance, allowing custom parsing and rendering rules to be defined.
 
 `ogImage` - Local path to an Open Graph image (e.g., `img/myImage.png`). This image will show up when your site is shared on Facebook and other websites/apps where the Open Graph protocol is supported.

lib/core/Head.js

@@ -66,6 +66,9 @@ class Head extends React.Component {
         {this.props.redirect && (
           <meta httpEquiv="refresh" content={`0; URL=${this.props.redirect}`} />
         )}
+        {this.props.config.manifest && (
+          <link rel="manifest" content={siteUrl + this.props.config.manifest} />
+        )}
         <link
           rel="shortcut icon"
           href={this.props.config.baseUrl + this.props.config.favicon}