Improve CookieParam.Expires documentation (#1336)

Author: kblok

lib/PuppeteerSharp/CookieParam.cs

@@ -39,7 +39,7 @@ public class CookieParam
         [JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
         public string Path { get; set; }
         /// <summary>
-        /// Gets or sets the expiration.
+        /// Gets or sets the expiration. Unix time in seconds.
         /// </summary>
         /// <value>Expiration.</value>
         [JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
@@ -74,4 +74,4 @@ public class CookieParam
         [JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
         public SameSite? SameSite { get; set; }
     }
-}
+}