add documentation about .native.js extensions

docs/platform-specific-code.md

@@ -98,9 +98,26 @@ BigButton.android.js
 You can then require the component as follows:
 
 ```javascript
-const BigButton = require('./BigButton');
+import BigButton from './BigButton';
 ```
 
 React Native will automatically pick up the right file based on the running platform.
 
-If you share your React Native code with a website, you might as well use the `BigButton.native.js` so that both iOS and Android will use this file, while the website will use `BigButton.js`.
+## Native-specific extensions (i.e. sharing code with NodeJS and Web)
+
+You can also use the `.native.js` extension when a module needs to be shared between NodeJS/Web and React Native but it has no Android/iOS differences. This is specially useful for projects that has common code shared among React Native and ReactJS.
+
+For example, say you have the following files in your project:
+
+```sh
+Container.js # picked up by Webpack, Rollup or any other Web bundler
+Container.native.js # picked up by the React Native bundler for both Android and iOS (Metro)
+```
+
+You can still require it without the `.native` extension, as follows:
+
+```javascript
+import Container from './Container';
+```
+
+**Pro tip:** Configure your Web bundler to ignore `.native.js` extensions in order to avoid having unused code in your production bundle, thus reducing the final bundle size.