adoc: add D-GSM chapter to osmohlr-usermanual

Change-Id: I392b5523870c2ef3267179160028d26f3f761b77
diff --git a/doc/manuals/osmohlr-usermanual.adoc b/doc/manuals/osmohlr-usermanual.adoc
index 7e709bd..68db1a7 100644
--- a/doc/manuals/osmohlr-usermanual.adoc
+++ b/doc/manuals/osmohlr-usermanual.adoc
@@ -24,6 +24,8 @@
 
 include::./common/chapters/control_if.adoc[]
 
+include::{srcdir}/chapters/dgsm.adoc[]
+
 include::./common/chapters/gsup.adoc[]
 
 include::./common/chapters/port_numbers.adoc[]