doc: Update memory requirements for FOP

Reported-by: Dave Page <dpage@pgadmin.org>

doc/src/sgml/docguide.sgml

@@ -336,11 +336,11 @@ checking for fop... fop
     file <filename>~/.foprc</filename>, for example:
 <programlisting>
 # FOP binary distribution
-FOP_OPTS='-Xmx1000m'
+FOP_OPTS='-Xmx1500m'
 # Debian
-JAVA_ARGS='-Xmx1000m'
+JAVA_ARGS='-Xmx1500m'
 # Red Hat
-ADDITIONAL_FLAGS='-Xmx1000m'
+ADDITIONAL_FLAGS='-Xmx1500m'
 </programlisting>
     There is a minimum amount of memory that is required, and to some extent
     more memory appears to make things a bit faster.  On systems with very