message: feat(devtools): add opening instructions
diff: <h4 class="header-text">Angular DevTools</h4>
  <div class="message">
  <img class="icon" src="/assets/check.png" />
  + <section>
  <p>Angular application running development mode.</p>
  + <p>Open developer tools, and select the Angular tab.</p>
  + </section>
  </div>
  </div>
  </body>
  