MC-15763: Introduce critical CSS scope loaded through head

- Stabilization

Author: vzabaznov

app/code/Magento/Theme/etc/adminhtml/system.xml

@@ -12,7 +12,9 @@
                 <field id="use_css_critical_path" translate="label comment" type="select" sortOrder="30" showInDefault="1" showInWebsite="1" showInStore="1" canRestore="1">
                     <label>Use CSS critical path</label>
                     <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
-                    <comment>CSS files are loading synchronously by default.</comment>
+                    <comment>
+                        <![CDATA[<strong style="color:red">Warning!</strong> Be sure that you have critical.css file for your theme. Other CSS files will be loaded asynchronously]]>
+                    </comment>
                 </field>
             </group>
         </section>