SEBA-386 Move VTN documentation to VTN repo

Change-Id: Iced66e84b04ad266dcfc20b147e8ede6ac174bd3
diff --git a/git_refs b/git_refs
index 8659fbc..9e9dd1a 100644
--- a/git_refs
+++ b/git_refs
@@ -28,4 +28,4 @@
 xos-gui               /docs    master
 xos-tosca             /docs    master
 xos                   /docs    master
-
+vtn-service           /docs    master