Linked libraries docs

Documentation to the 2.5 feature that allows sites to add links in the
catalog from copy details area of the catalog.

Signed-off-by: Kathy Lussier <klussier@masslnc.org>
Library information pages

Updating the linked libraries documentation to include details on the new
library information pages introduced in 2.6.

Signed-off-by: Kathy Lussier <klussier@masslnc.org>