pgsql: Add small example about pg_archivecleanup -x option

Add small example about pg_archivecleanup -x option

Every time I read this I had doubts about whether the argument to the
-x option should include the dot (yes).  A small example should
clarify this.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/92a953fbf8c90c3b316fbc275767efb6994f1589

Modified Files
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doc/src/sgml/pgarchivecleanup.sgml |    7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)