title: why groups in <menuitem groups=''> tag and purpose in odoo 11
body: <p>I am trying to create custom module in odoo11, bit confused about <strong>groups</strong> attribute in menuitem.</p>
  
  <pre><code>&lt;menuitem id="product_menu_catalog"
            name="Catalog"
            action="product.product_template_action"
            parent="sale_menu_root"
            sequence="4"
           groups="sales_team.group_sale_salesman"
  /&gt;
  </code></pre>