Doc: Fix ambuiguity in column lists.
The behavior for columns added later to the table for publications with no
specified column lists was not clear.
Reported-by: Koen De Groote
Author: Peter Smith
Reviewed-by: Vignesh C, Laurenz Albe
Backpatch-through: 15
Discussion: https://postgr.es/m/
171621878740.686.
11325940592820985181@wrigleys.postgresql.org