docs: update Certification field descriptions

PiperOrigin-RevId: 665432329

google/shopping/css/v1/css_product_common.proto

@@ -207,15 +207,22 @@ message Attributes {
   optional string custom_label_4 = 50;
 }
 
-// The certification for the product.
+// The certification for the product. Use the this attribute to describe
+// certifications, such as energy efficiency ratings, associated with a product.
 message Certification {
-  // Name of the certification.
+  // The name of the certification. At this time, the most common value is
+  // "EPREL", which represents energy efficiency certifications in the EU
+  // European Registry for Energy Labeling (EPREL) database.
   string name = 1;
 
-  // Name of the certification body.
+  // The authority or certification body responsible for issuing the
+  // certification. At this time, the most common value is "EC" or
+  // “European_Commission” for energy labels in the EU.
   string authority = 2;
 
-  // A unique code to identify the certification.
+  // The code of the certification. For example, for the EPREL certificate with
+  // the link https://eprel.ec.europa.eu/screen/product/dishwashers2019/123456
+  // the code is 123456. The code is required for European Energy Labels.
   string code = 3;
 }