nat: Add an example for a black list
diff --git a/openbsc/doc/examples/osmo-bsc_nat/black-list.cfg b/openbsc/doc/examples/osmo-bsc_nat/black-list.cfg
new file mode 100644
index 0000000..d36179d
--- /dev/null
+++ b/openbsc/doc/examples/osmo-bsc_nat/black-list.cfg
@@ -0,0 +1 @@
+678012512671923:6:6: