docs(plugins): document regexp for splitChunks.chunks (webpack#6888)

* docs(plugins): document regexp for splitChunks.chunks

* Update src/content/plugins/split-chunks-plugin.mdx

Co-authored-by: Nitin Kumar <[email protected]>

---------

Co-authored-by: Nitin Kumar <[email protected]>

Author: chenxsan

src/content/plugins/split-chunks-plugin.mdx

@@ -98,7 +98,7 @@ By default webpack will generate names using origin and name of the chunk (e.g.
 
 ### splitChunks.chunks
 
-`string = 'async'` `function (chunk)`
+`string = 'async'` `function (chunk)` `RegExp`
 
 This indicates which chunks will be selected for optimization. When a string is provided, valid values are `all`, `async`, and `initial`. Providing `all` can be particularly powerful, because it means that chunks can be shared even between async and non-async chunks.
 
@@ -134,6 +134,19 @@ module.exports = {
 };
 ```
 
+If you are using webpack version 5.86.0 or later, you can also pass a regular expression:
+
+```js
+module.exports = {
+  //...
+  optimization: {
+    splitChunks: {
+      chunks: /foo/,
+    },
+  },
+};
+```
+
 T> You can combine this configuration with the [HtmlWebpackPlugin](/plugins/html-webpack-plugin/). It will inject all the generated vendor chunks for you.
 
 ### splitChunks.maxAsyncRequests