odoo-survey-addons/survey_description/views/survey_survey.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

  <record id="survey_survey_form" model="ir.ui.view">
    <field name="name">survey_description survey.survey form</field>
    <field name="model">survey.survey</field>
    <field name="inherit_id" ref="survey.survey_form"/>
    <field name="priority">20</field>
    <field name="arch" type="xml">
      <xpath expr="//notebook/page[descendant::field[@name='page_ids']]" position="after">
        <page name="description" string="Description">
          <group>
            <p colspan="2" class="text-muted oe_edit_only">
              This content will be displayed between the title of the survey and the "Start" button, on the answer homepage.<br/>
              You can also add a custom content on each page of the survey through the "Description" field on each page.
            </p>
            <field name="description" nolabel="1" colspan="2"/>
          </group>
        </page>
        <page name="thank_you" string="Thank you page">
          <group class="o_label_nowrap">
            <field name="thank_you_message"/>
          </group>
        </page>
      </xpath>
    </field>
  </record>

</odoo>