docs(v2): mention that plugin-ideal-image only perform compression …

…on a production build (#2572)

* Add a note that `plugin-ideal-image` only perform compression on a production build. 

In reference to #2571

* Update using-plugins.md

* Update using-plugins.md

* Update using-plugins.md

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

website/docs/using-plugins.md

@@ -403,26 +403,25 @@ module.exports = {
 
 ### `@docusaurus/plugin-ideal-image`
 
-Docusaurus Plugin to generate an almost ideal image (responsive, lazy-loading, and low quality placeholder)
+Docusaurus Plugin to generate an almost ideal image (responsive, lazy-loading, and low quality placeholder) **in the production builds**.
 
 ```bash npm2yarn
 npm install --save @docusaurus/plugin-ideal-image
 ```
 
 Modify your `docusaurus.config.js`
 
-```js title="docusaurus.config.js"
+```diff
 module.exports = {
-  // ...
-  // highlight-next-line
-  plugins: ['@docusaurus/plugin-ideal-image'],
-  // ...
-};
+  ...
++ plugins: ['@docusaurus/plugin-ideal-image'],
+  ...
+}
 ```
 
 #### Usage
 
-This plugin supports png, gif and jpg only
+This plugin supports the PNG, GIF and JPG formats only.
 
 ```jsx
 import Image from '@theme/IdealImage';

website/versioned_docs/version-2.0.0-alpha.50/using-plugins.md

@@ -394,7 +394,7 @@ module.exports = {
 
 ### `@docusaurus/plugin-ideal-image`
 
-Docusaurus Plugin to generate an almost ideal image (responsive, lazy-loading, and low quality placeholder)
+Docusaurus Plugin to generate an almost ideal image (responsive, lazy-loading, and low quality placeholder) **in the production builds**.
 
 ```bash npm2yarn
 npm install --save @docusaurus/plugin-ideal-image
@@ -412,7 +412,7 @@ module.exports = {
 
 #### Usage
 
-This plugin supports png, gif and jpg only
+This plugin supports the PNG, GIF and JPG formats only.
 
 ```jsx
 import Image from '@theme/IdealImage';