Update HOWTO.md

HOWTO.md

@@ -66,6 +66,16 @@
     ]
     ```
 
+    In the [SETTINGS] section enable the layers you want to create. By default NVDCT will onyl create the CDP layer.
+
+    ```
+    # settings equivalent to CLI options
+    [SETTINGS]
+    # layers = ["LLDP", "CDP", "STATIC", "CUSTOM", "L3v4"]
+    layers = ["LLDP", "L3v4"]
+    ```
+
+
 
 1. Create the topology data