Updating doc references

Issue-ID: CCSDK-2846
Signed-off-by: Singal, Kapil (ks220y) <ks220y@att.com>
Change-Id: Ia32c855dc48549a50933849a260e3d4d86b98adf
diff --git a/docs/modelingconcepts/external-system.rst b/docs/modelingconcepts/external-system.rst
index 806600f..598cd45 100644
--- a/docs/modelingconcepts/external-system.rst
+++ b/docs/modelingconcepts/external-system.rst
@@ -3,6 +3,8 @@
 .. International License. http://creativecommons.org/licenses/by/4.0
 .. Copyright (C) 2020 Deutsche Telekom AG.
 
+.. _external_system:
+
 External Systems support
 ------------------------