Allow to be used with netbox docker containers

[ftaeger]

Some of us use the netbox docker containers from https://github.com/netbox-community/netbox-docker

I am not sure how the proxbox plugin would be installed in this case so maybe a little help from the community and some documentation here in the readme would be a good thing.

[emersonfelipesp]

Plugin isn't recognized by netbox #58 has some insights about it.

[stijnpieters]

The following guide might help in getting plugins working in Netbox Docker.
https://github.com/netbox-community/netbox-docker/wiki/Using-Netbox-Plugins

Following a fairly default setup the plugin seems to be working on Netbox Docker v3.4.8

small edit: plugin configuration goes in configuration/plugins.py

[emersonfelipesp]

I will review it, but probably will be release as has already been marked to v0.0.8 only!

[emersonfelipesp]

#195