docs: improve polyfill warning

Author: Akryum

README.md

@@ -23,7 +23,7 @@ Smooth scroll with any amount of data ([demo](https://akryum.github.io/vue-virtu
 npm install --save vue-virtual-scroller
 ```
 
-**⚠️ `vue-virtual-scroller` now uses [vue-observe-visibility](https://github.com/Akryum/vue-observe-visibility#installation) to automatically refresh itself when shown to prevent display glitches. This means you need to include the polyfills needed by `vue-observe-visibility` for this to work.**
+**⚠️ `vue-virtual-scroller` now uses [vue-observe-visibility](https://github.com/Akryum/vue-observe-visibility#installation) to automatically refresh itself when shown to prevent display glitches. This means you need to include the [Intersection Observer polyfill](https://github.com/w3c/IntersectionObserver/tree/master/polyfill) needed by `vue-observe-visibility` for this to work in old browsers (like Internet Explorer).**
 
 ## Default import