Fix missing ports line in override

Using-Netbox-Plugins.md

@@ -45,6 +45,7 @@ RUN /opt/netbox/venv/bin/pip install  --no-warn-script-location -r /plugin_requi
 version: '3.4'
 services:
   netbox:
+    ports:
       - 8000:8080
     build:
       context: .