Обсуждение: pgsql: doc: clarify that storage parameter values are optional

doc:  clarify that storage parameter values are optional

In a few cases, the documented syntax specified storage parameter values
as required.

Reported-by: galiev_mr@taximaxim.ru

Discussion: https://postgr.es/m/159283163235.684.4482737698910467437@wrigleys.postgresql.org

Backpatch-through: 9.5

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/81b244e78b637b16ddb7a33bc5fb7448b6c45c39

Modified Files
--------------
doc/src/sgml/ref/alter_index.sgml             | 4 ++--
doc/src/sgml/ref/alter_materialized_view.sgml | 2 +-
doc/src/sgml/ref/alter_table.sgml             | 4 ++--
doc/src/sgml/ref/create_index.sgml            | 2 +-
4 files changed, 6 insertions(+), 6 deletions(-)