Document issue about "CREATE MATERIALIZED VIEW"

https://github.com/cloudberrydb/cloudberrydb-site/blob/cbdb-doc-validation/docs/sql-stmts/sql-stmt-create-materialized-view.md

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CREATE MATERIALIZED VIEW [ IF NOT EXISTS ]
[ ( [, ...] ) ]
[ USING ]
[ WITH ( [= ] [, ... ] ) ]
[ TABLESPACE ]
AS
[ WITH [ NO ] DATA ]
[DISTRIBUTED {| BY [], [ ... ] | RANDOMLY | REPLICATED }]

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DISTRIBUTED clause is not correct. Missing '(' and '|' should not be in front of 'BY'.

The following is an actual example tried on CBDB.

gpadmin=# CREATE MATERIALIZED VIEW mt11 (mc1, mc2, mc3) as select c1,c2,c3 from t1 distributed by (mc1 int4_ops,mc2 text_ops);
SELECT 4