Better documentation regarding the webhook object

Co-Authored-By: SubZero0 <pnmanjos@hotmail.com>

src/Discord.Net.Rest/Entities/AuditLogs/DataTypes/WebhookCreateAuditLogData.cs

@@ -43,7 +43,7 @@ namespace Discord.Rest
         ///     Gets the webhook that was created if it still exists.
         /// </summary>
         /// <returns>
-        ///     A webhook object representing the webhook that was created if it still exists.
+        ///     A webhook object representing the webhook that was created if it still exists, otherwise returns <c>null</c>.
         /// </returns>
         public IWebhook Webhook { get; }