commands/listplaylist: add note about format

src/commands/stored_playlists/listplaylist.rs

@@ -62,6 +62,7 @@ impl CommandRequest<'_> for ListPlaylistRequest {
     }
 }
 
+// NOTE: this is actually supposed to be Vec<DbSongInfo>
 multi_item_command_response!(ListPlaylist, "file", PathBuf);
 
 impl Command<'_, '_> for ListPlaylist {