gbproxy-usermanual: Explain BSSGP/BVC handling

Related: SYS#5005
Change-Id: I383fcd3864a94177f13909c6b8c15648900d3201
diff --git a/doc/manuals/osmogbproxy-usermanual.adoc b/doc/manuals/osmogbproxy-usermanual.adoc
index c4e0b9d..c93ebec 100644
--- a/doc/manuals/osmogbproxy-usermanual.adoc
+++ b/doc/manuals/osmogbproxy-usermanual.adoc
@@ -9,6 +9,8 @@
 
 include::{srcdir}/chapters/gbproxy-overview.adoc[]
 
+include::{srcdir}/chapters/gbproxy-details.adoc[]
+
 include::{srcdir}/chapters/gbproxy-running.adoc[]
 
 include::{srcdir}/chapters/gbproxy-control.adoc[]