Any executable files (or symlinks to executable files) found in this
directory will be run by genup at the end of its main process (unless
suppressed by the --no-custom-updaters option).

You can use this if you need to extend genup's functionality. Note that only
files or links at the top level (not subdirectories) will be processed, and
that if any such custom updater returns with a non-zero exit status, genup will
also exit (immediately) with an error.