Add doc about polyfill

Author: Th1nkK1D

docs/using.stories.mdx

@@ -84,3 +84,7 @@ For example with `navbar` component:
 ```
 
 Available components and coresponded properties can be found in the **COMPONENTS** section on the left panel.
+
+### (Optional) Add polyfill for legacy browser
+
+To support [browsers without Web Components implementation](https://developer.mozilla.org/en-US/docs/Web/Web_Components#browser_compatibility), please use [Web Components polyfill](https://github.com/webcomponents/polyfills)