pgsql: doc: clarify "state" table reference in tutorial

doc: clarify "state" table reference in tutorial

Reported-by: Vyacheslav Shablistyy

Discussion: /messages/by-id/159586122762.680.1361378513036616007@wrigleys.postgresql.org

Backpatch-through: 9.5

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a6775352476ac92d6b3eb3ae2dfd2775e3622afe

Modified Files
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doc/src/sgml/advanced.sgml | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)