feat: added a link to MDN JS guide

Close #1837

Author: NataliaTepluhina

src/guide/introduction.md

@@ -71,7 +71,7 @@ The above example demonstrates the two core features of Vue:
 You may already have questions - don't worry. We will cover every little detail in the rest of the documentation. For now, please read along so you can have a high-level understanding of what Vue offers.
 
 :::tip Prerequisites
-The rest of the documentation assumes basic familiarity with HTML, CSS and JavaScript. If you are totally new to frontend development, it might not be the best idea to jump right into a framework as your first step - grasp the basics and then come back! Prior experience with other frameworks helps, but is not required.
+The rest of the documentation assumes basic familiarity with HTML, CSS and JavaScript. If you are totally new to frontend development, it might not be the best idea to jump right into a framework as your first step - grasp the basics and then come back! You can check your knowledge level with [this JavaScript overview](https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript). Prior experience with other frameworks helps, but is not required.
 :::
 
 ## The Progressive Framework