pgsql: doc: requirepeer is a way to avoid spoofing

doc:  requirepeer is a way to avoid spoofing

We already mentioned unix_socket_directories as an option.

Reported-by: https://www.postgresql.org/message-id/45016837-6cf3-3136-f959-763d06a28076%402ndquadrant.com

Backpatch-through: 9.6

Branch
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REL9_6_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/2b4ae9c29d42ce7b1b7bb947c585b78a21535aa2

Modified Files
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doc/src/sgml/runtime.sgml | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)