Add link to troubleshooting guide in UP4

Change-Id: I18c6ae3f63a3e38e0dcd66df1692c08bc2045318
diff --git a/advanced/upf.rst b/advanced/upf.rst
index 94cac1f..e92e831 100644
--- a/advanced/upf.rst
+++ b/advanced/upf.rst
@@ -217,9 +217,7 @@
 UP4 Troubleshooting
 -------------------
 
-``TODO Daniele``
-
-Example of UP4 CLI commands to debug the state of UP4.
+See :ref:`troubleshooting_guide`.
 
 DBUF
 ----