docs(v2): add plugin redirects production build note (#2983)

* add plugin redirects production build note

* Update using-plugins.md

Co-authored-by: Yangshun Tay <tay.yang.shun@gmail.com>

website/docs/using-plugins.md

@@ -84,10 +84,14 @@ A plugin is a module which exports a function that takes two parameters and retu
 
 The exported modules for plugins are called with two parameters: `context` and `options` and returns a JavaScript object with defining the [lifecycle APIs](./lifecycle-apis.md).
 
-For example if you have a reference to a local folder such as this in your
+For example if you have a reference to a local folder such as this in your `docusaurus.config.js`:
-docusaurus.config.js:
 
-    plugins: [path.resolve(__dirname, 'my-plugin')],
+```js title="docusaurus.config.js"
+module.exports = {
+  // ...
+  plugins: [path.resolve(__dirname, 'my-plugin')],
+};
+```
 
 Then in the folder `my-plugin` you can create an index.js such as this
 
@@ -103,8 +107,7 @@ module.exports = function(context, options) {
 };
 ```
 
-The `my-plugin` folder could also be a fully fledged package with it's own 
+The `my-plugin` folder could also be a fully fledged package with it's own package.json and a `src/index.js` file for example
-package.json and a `src/index.js` file for example
 
 #### `context`
 
@@ -475,6 +478,12 @@ Docusaurus Plugin to generate **client-side redirects**.
 
 This plugin will write additional HTML pages to your static site, that redirects the user to your existing Docusaurus pages with JavaScript.
 
+:::note
+
+This plugin only create redirects for the production build.
+
+:::
+
 :::caution
 
 It is better to use server-side redirects whenever possible.