title: Adding a default value to text-input in simple-form
body: <p>I want to add a default value to a text-input field using simple-form.
  With <code>:placeholder</code> it is not used as default....</p>
  <pre><code>&lt;%= f.input :user, :placeholder =&gt; 'user@example.com' %&gt;
  </code></pre>