Adds 'Vue Router for Everyone' course. (#4994)

Adds the free 'Vue Router for Everyone' course on Vue.js from https://vueschool.io.

free-courses-en.md

@@ -391,6 +391,7 @@
 * [Internationalization with vue-i18n](https://vueschool.io/courses/internationalization-with-vue-i18n)
 * [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)
+* [Vue Router for Everyone](https://vueschool.io/courses/vue-router-for-everyone)
 * [Vue.js Fundamentals](https://vueschool.io/courses/vuejs-fundamentals)
 * [Vuex for Everyone](https://vueschool.io/courses/vuex-for-everyone)