fdo#71652 - change thousand separate description

Minor change to the text found in thousand separator parameter use
description to make it a bit clearer.

Change-Id: Idfa83e04c123458913af0795c78ea4fae616e24c
Reviewed-on: https://gerrit.libreoffice.org/6690
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>