title: Simple example: Property or method "sayHello" is not defined on the instance but referenced during render
body: <p>I'm following a vue course on udemy.
  It's a super simple example, but I get the error <code>Property or method "sayHello" is not defined on the instance but referenced during render.</code>.</p>
  
  <p>I have an easy setup in vscode with two files: <code>index.html</code> and <code>script.js</code>, I run <code>index.html</code> in the browser</p>
  
  <p>index.html</p>
  
  <pre><code>&lt;div id="app"&gt;
      &lt;p&gt;{{title}}&lt;/p&gt;
      &lt;p&gt;{{sayHello()}}&lt;/p&gt;
  &lt;/div&gt;
  
  
  
  &lt;script src="https://unpkg.com/vue/dist/vue.js"&gt;&lt;/script&gt;
  &lt;script src="C:\Users\[my name]\dev\Vue JS 2 - The Complete Guide (incl. Vue Router &amp; Vuex\section01\script.js"&gt;&lt;/script&gt;
  </code></pre>
  
  <p>script.js</p>
  
  <pre><code>new Vue({
      el: '#app',
      data: {
          title: 'Hello World!'
      },
      methods: {
          sayHello: function () {
              return 'Hello Methods!';
          }
      }
  });
  
  </code></pre>
  
  <p>What am I doing wrong?</p>