fdo#79216 correct description of NORM.S.DIST function

Change-Id: I5b95e4d648793253b0ac3c5ccd4019a145a3e762
Reviewed-on: https://gerrit.libreoffice.org/9839
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>