Обсуждение: pgsql: pg_upgrade: improve docs about extension upgrades

pg_upgrade:  improve docs about extension upgrades

The previous wording was unclear about the steps needed to upgrade
extensions, and how to update them after pg_upgrade.

Reported-by: Dave Cramer

Discussion: https://postgr.es/m/CADK3HHKawwbOcGwMGnDuAf3-U8YfvTcS8jqDv3UM=niijs3MMA@mail.gmail.com

Backpatch-through: 9.6

Branch
------
REL_11_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/cc7091d91aecf067082e06bbe9359b507c0dd1c4

Modified Files
--------------
doc/src/sgml/ref/pgupgrade.sgml | 32 +++++++++++++++++++++-----------
1 file changed, 21 insertions(+), 11 deletions(-)