docs: modern js usage example

README.md

@@ -58,7 +58,7 @@ javascript:(function () { var script = document.createElement('script'); script.
 You can get it on npm.
 
 ```bash
-npm install eruda --save
+npm install eruda --save-dev
 ```
 
 Add this script to your page.
@@ -86,6 +86,14 @@ The JavaScript file size is quite huge(about 100kb gzipped) and therefore not su
 })();
 ```
 
+If you are using modern JavaScript tooling, you can dynamically import it.
+
+```javascript
+if (import.meta.env.MODE === 'development') {
+    import('eruda').then(eruda => eruda.default.init());
+}
+```
+
 ## Configuration
 
 When initialization, a configuration object can be passed in.