Adding a separate set of modules to serve as an incubator for new core API & implementations.

Change-Id: Ic7df5243ea18dec4f96f47dd2cf922e33827f4de
diff --git a/docs/external.xml b/docs/external.xml
index 15b0897..60d72b7 100644
--- a/docs/external.xml
+++ b/docs/external.xml
@@ -65,6 +65,12 @@
                                 org.onlab.*
                             </packages>
                         </group>
+                        <group>
+                            <title>Incubator for Network Model &amp; Services</title>
+                            <packages>
+                                org.onosproject.incubator:org.onosproject.exp.*
+                            </packages>
+                        </group>
                     </groups>
                 </configuration>
             </plugin>