manual: Update manuals, include sgsn pooling and NS variants

Related: SYS#5005, SYS#5115, OS#4523
Change-Id: I440b0f9a6e18c21b11640ca32403f19d7e83b5c1
diff --git a/doc/manuals/osmogbproxy-usermanual.adoc b/doc/manuals/osmogbproxy-usermanual.adoc
index bf2404d..06bc098 100644
--- a/doc/manuals/osmogbproxy-usermanual.adoc
+++ b/doc/manuals/osmogbproxy-usermanual.adoc
@@ -21,6 +21,10 @@
 
 include::{srcdir}/chapters/gbproxy-configuration.adoc[]
 
+include::{srcdir}/chapters/gbproxy-sgsnpool.adoc[]
+
+include::./common/chapters/gb-variants.adoc[]
+
 include::./common/chapters/gb.adoc[]
 
 include::./common/chapters/control_if.adoc[]