Docs: Update to "org unit" terminology in nav.adoc

Author: spmorrison

docs/modules/admin_initial_setup/nav.adoc

@@ -13,7 +13,7 @@
 *** xref:opac:new_skin_customizations.adoc[Creating a New Skin: the Bare Minimum]
 *** xref:admin_initial_setup:carousels.adoc[OPAC Carousels]
 *** xref:admin_initial_setup:managing_holds_ui_in_tpac.adoc[Managing how holds options display in the catalog]
-*** xref:admin_initial_setup:custom_ou_trees.adoc[Custom Org Unit Trees]
+*** xref:admin_initial_setup:custom_ou_trees.adoc[Custom Organizational Unit Trees]
 ** xref:admin_initial_setup:KidsOPAC.adoc[Kid's OPAC Configuration]
 ** xref:admin_initial_setup:bootstrap_opac.adoc[Bootstrap OPAC]
 ** xref:admin:search_interface.adoc[Designing the patron search experience]