make.conf.5: Suggest PORTAGE_LOG_FILTER_FILE_CMD supervisor for cat fallback (bug 781854)

If PORTAGE_LOG_FILTER_FILE_CMD fails after exec, then output
will be lost. Therefore, suggest to use bash as a supervisor,
with fallback to cat.

Bug: https://bugs.gentoo.org/781854
Signed-off-by: Zac Medico <zmedico@gentoo.org>
1 file changed