Extra: CDN only 41 / 42
.vue files require your code to be compiled. If you work on a very simple website, you might get away with only the CDN build.
At the bottom, we load Vue through a CDN script, new up an instance of Vue, and mount it on the element #app.
Since this is a HTML file, it would literally render {{ hello }} until Vue is initialized. That's why there is the v-cloak attribute, which Vue will detect and remove for us.