Adding and fixing javados.

Change-Id: I38eddb0b11630cdd83c5d1e5d5dc393ee2555897
diff --git a/docs/src/main/javadoc/overview.html b/docs/src/main/javadoc/overview.html
index a3e32d9..d3712ab 100644
--- a/docs/src/main/javadoc/overview.html
+++ b/docs/src/main/javadoc/overview.html
@@ -39,7 +39,15 @@
 </p>
 
 <p>
-    The following diagram describes a general structure of each ONOS subsystem:
+    The figure below provides a visual inventory of the various ONOS subsystems.
+    The ones with the gray outline represent either work in progress features
+    planned for release in 2015.<br>
+    <img src="doc-files/onos-subsystems.png" alt="ONOS architecture tiers">
+
+</p>
+
+<p>
+    The following diagram describes the general structure of each ONOS subsystem:
     <br>
     <img src="doc-files/onos-subsystem.png" alt="ONOS subsystem structure"><br>
     For example, the device-subsystem comprises of a core