Add dark mode section inside the readme

Author: mdubus

README.md

@@ -111,13 +111,30 @@ module.exports = {
         maxSuggestions: 10, // Default: 5
         hotKeys: [], // Default: ['s', '/']
         cropLength: 50, // Default: 30
-        layout: 'simple' // Default: "columns"
+        layout: 'simple', // Default: "columns"
+        enableDarkMode: true // Default: false
       }
     ]
   ]
 }
 ```
 
+#### Dark mode
+
+You can enable dark mode by adding `enableDarkMode: true` to your configuration file.
+
+To override the default theme of the searchbar, you can edit your `.vuepress/styles/palette.styl` file.
+A few variables are available :
+
+```js
+$msAccentDarkColor
+$msInputDarkBgColor
+$msTextDarkColor
+$borderDarkColor
+```
+
+You can also find an example in our [playground's `palette.styl` file](./playground/.vuepress/styles/palette.styl)
+
 ## Compatibility with MeiliSearch
 
 This package only guarantees the compatibility with the [version v0.20.0 of MeiliSearch](https://github.com/meilisearch/MeiliSearch/releases/tag/v0.20.0).