pgsql: doc:: simplify introductory text

doc:: simplify introductory text

Reported-by: Joshua D. Drake

Discussion: /messages/by-id/5ac2c96d-37a6-18aa-08c4-327a6fbff24b@commandprompt.com

Author: Joshua D. Drake

Backpatch-through: master

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/322f55bdbd018bf18a0c5605c7bc592c625dc263

Modified Files
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doc/src/sgml/postgres.sgml | 94 ++++++++++++++++++++++------------------------
1 file changed, 45 insertions(+), 49 deletions(-)