pgsql: README: add URLs for openldap installation

README: add URLs for openldap installation

Reported-by: Michael Paquier

Discussion: /messages/by-id/20180521013425.GA4476@paquier.xyz

Backpatch-through: head

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9bab9cb36ad9186c9898703106b545d6dbb2aa24

Modified Files
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src/test/ldap/README | 11 +++++++++++
1 file changed, 11 insertions(+)