add error message when passwords don't match

templates/user/create_user.twig

@@ -20,6 +20,14 @@
     </div>
     <div class="field">
         <input type="password" name="confirmpassword" id="confirmpassword" placeholder="Confirm your password" required>
+        {% if message %}
+        <div class="ui warning message">
+            <div class="header">Could you check something!</div>
+            <ul class="list">
+                <li>{{message}}</li>
+            </ul>
+        </div>
+        {% endif %}
     </div>
     <div class="field">
         <input type="email" name="mail" id="mail" placeholder="Email" value="{{mail}}" required>