mined.1: Move some info from CAVEATS to DESCRIPTION.

mandoc(1) warns about CAVEATS not being in conventional order and
silencing it by moving the section would have caused it to be behind
HISTORY even.

However, the info is more important than the editor's history, so
instead add it to the DESCRIPTION, which is short in this case, anyway.

Reported-by:   Eitan Adler <eadler@freebsd.org>
Dragonfly-bug: <http://bugs.dragonflybsd.org/issues/2540>
mined(1): Fix alignment issue on strict alignment architectures.

Reported-by:   Eitan Adler <eadler@freebsd.org>
Dragonfly-bug: <http://bugs.dragonflybsd.org/issues/2541>