[SDFAB-595] Add UPF configuration guide

Change-Id: I59cb4bd229f70dd334ffb1e3597764374adf4df7
diff --git a/advanced/upf.rst b/advanced/upf.rst
index 72c9ae7..8298898 100644
--- a/advanced/upf.rst
+++ b/advanced/upf.rst
@@ -1,2 +1,8 @@
 User Plane Function (UPF)
 =========================
+
+.. toctree::
+   :maxdepth: 2
+   :glob:
+
+   upf_configuration