Add reference to STC tests in UP4 repo

Change-Id: I72dc7ea594d7b06d46e6fdea2a8ea23319780b79
diff --git a/conf.py b/conf.py
index e3a51e3..10209bd 100644
--- a/conf.py
+++ b/conf.py
@@ -243,8 +243,9 @@
 # -- Options for linkcheck ---------------------------------------------------
 # The link checker strips off .md from links and then complains
 linkcheck_ignore = [
-    r'https://github.com/stratum/fabric-tna/*',  # Ignore link of private repos
-    r'https://github.com/opennetworkinglab/sdfabric-utils', # Private repo
+    r'https://github.com/stratum/fabric-tna/*',  # Fabric-TNA private repo
+    r'https://github.com/opennetworkinglab/sdfabric-utils',  # Private repo
+    r'https://github.com/omec-project/up4/*'  # UP4 private repo
 ]
 
 linkcheck_timeout = 3