pgsql: doc: Add timeline as valid recovery target in standby.signal doc

doc: Add timeline as valid recovery target in standby.signal documentation

The documentation states that no target settings will be used when
standby.signal is present, but this is not quite the case since
recovery_target_timeline is a valid recovery target for a standby.

Update the documentation with this exception.

Author: David Steele <david@pgmasters.net>
Discussion: https://www.postgresql.org/message-id/flat/e445616d-023e-a268-8aa1-67b8b335340c%40pgmasters.net

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/775578a445bbbbfc43b1dcc1c3e2d3b4bdb35962

Modified Files
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doc/src/sgml/config.sgml | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)