created preentry script to help with local development

docker/preentry.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+set -e
+
+# Example of how to activate a development plugin
+
+# echo -e "installing custom plugin"
+# source /opt/netbox/venv/bin/activate
+# cd /opt/plugin_source
+# python3 setup.py develop
+# echo -e "finished installing custom plugin"
+
+
+# follow on scripts expect this to be the current dir. 
+# uncomment if you have changed directory
+# cd /opt/netbox/netbox
+exec "$@"