column: Address fill-order confusion in documentation

column: Address fill-order confusion in documentation

Historical versions of column have described the default fill order as
rows-then-columns and the -x order as columns-then-rows. This was
misleading at best, and the util-linux implementation was updated to
clarify the actual behaviour in 3e094e5fe2 (March 2017).

However, the other implementations (used by *BSD, macOS, Debian, &al.)
continue to use the previous wording, and a user comparing them could
easily get the false impression that util-linux column has exactly the
opposite fill behaviour from BSD column.

To address this, a note is added to the man page explaining the change
and clarifying that, despite what the BSD documentation says, the two
implementations behave identically in this regard.

Signed-off-by: dana <dana@dana.is>