README: Remove the list of additional fields.
README: Remove the list of additional fields.

The list of additional fields will be maintained elsewhere in the
documentation (in the man page), remove it from the README, as it was
outdated anyway.

Signed-off-by: Gergely Nagy <6780fac3b38619ac20422286e4110a70dbba2203@balabit.hu>

deirf/libumberlog