Bug 29764: Fix incorrect EmbedItems RecordProcessor filter POD

Bug 29764: Fix incorrect EmbedItems RecordProcessor filter POD

This patch makes the usage POD for the EmbedItems filter actually be
usable. The filter is used in opac-ISBDdetail.pl and the POD is updated
to how it is used there.

Not much to test.

Signed-off-by: David Cook <dcook@prosentient.com.au>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 47c01f0b8a181a2d6f31478d08d9a3ee728e7fe4)

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>