pgsql: In the release notes, mention that the "Overview" items are

Log Message:
-----------
In the release notes, mention that the "Overview" items are listed in
the sections below in more detail.

Modified Files:
--------------
pgsql/doc/src/sgml:
release.sgml (r1.562 -> r1.563)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/release.sgml?r1=1.562&r2=1.563)