add banner with survey to docs (#1729)

Author: OriolAbril

doc/_templates/layout.html

@@ -24,3 +24,14 @@
     {{ super() }}
   {% endif %}
 {% endblock %}
+
+<!-- Add banner to all pages! -->
+{%- block scripts_end %}
+{{ super() }}
+<script>
+  $(document).ready(function () {
+    const content = $('<div class="alert-info">Help us improve our documentation answering this  <a href="https://docs.google.com/forms/d/e/1FAIpQLSdm98VJvKad6V7V-s6Dg5vk34Dyc17fnFBtAOBcaaQ7In7eUw/viewform">~2min survey</a></div>')
+    $('#banner').append(content);
+  })
+</script>
+{%- endblock %}