pgsql: doc: clarify handling of time zones with "time with time zone"

doc: clarify handling of time zones with "time with time zone"

Reported-by: davecramer@postgres.rocks

Discussion: /messages/by-id/168451942371.714.9173574930845904336@wrigleys.postgresql.org

Backpatch-through: 11

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/cc067621416687b56e0b536c51710b4ae456f2bc

Modified Files
--------------
doc/src/sgml/datatype.sgml | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)