add fixme re exif times

Program.cs

@@ -333,6 +333,7 @@ public class Photo {
       }
     }
 
+    // FIXME: there is also a SubSecTimeOriginal tag we could use to get fractional seconds.
     // FIXME: I think the iPhone stores time in UTC but other cameras report it in local time.
     IExifValue<string>? dateTimeOriginal;
     if (exifs.TryGetValue(ExifTag.DateTimeOriginal, out dateTimeOriginal)) {