Updating gNB Simulator documentation

Updated supported procedure lists, added block diagram and added
reference to the release 1.0 file.

Change-Id: Ifb8d3fb7042fac04f89bd71c12d5185c300c0b8c
diff --git a/developer/gnbsim.rst b/developer/gnbsim.rst
index 043d230..cf8eb40 100644
--- a/developer/gnbsim.rst
+++ b/developer/gnbsim.rst
@@ -6,6 +6,9 @@
 gNB Simulator
 =============
 
+.. image:: ../_static/images/gNBSim.png
+  :width: 700px
+
 Description
 -----------
 The gNB Sim tool simulates gNodeB and UE by generating and processing NAS and
@@ -15,6 +18,7 @@
 * Registration
 * UE initiated PDU Session Establishment
 * UE Initiated De-registration.
+* AN Release
 
 It is also capable to generate and send user data packets (ICMP echo request)
 and process down-link user data (ICMP echo response) over the established data