Add Intro to Vue 2 course (#4046)

free-courses-en.md

@@ -308,6 +308,7 @@
 
 #### Vue.js
 
+* [Intro to Vue 2](https://www.vuemastery.com/courses/intro-to-vue-js/vue-instance)
 * [Intro to Vue 3](https://www.vuemastery.com/courses/intro-to-vue-3/intro-to-vue3)