pgsql: Reorganize Notes section in documentation of pg_checksums

Reorganize Notes section in documentation of pg_checksums

This commit reorders the paragraphs of the Notes section in order of
importance, and clarifies better the safe uses of pg_checksums for
replication setups.

Author: Fabien Coelho
Discussion: https://postgr.es/m/alpine.DEB.2.21.1903231404280.18811@lancre

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a7cc52370b2b8a0f9883e299cb07f56d702b58c2

Modified Files
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doc/src/sgml/ref/pg_checksums.sgml | 38 ++++++++++++++++++--------------------
1 file changed, 18 insertions(+), 20 deletions(-)