pgsql: Document that doc builds now build indexes by default, unless

Log Message:
-----------
Document that doc builds now build indexes by default, unless "draft" is
used.

Modified Files:
--------------
pgsql/doc/src/sgml:
release.sgml (r1.554 -> r1.555)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/release.sgml?r1=1.554&r2=1.555)