Add note about url name rule

[miyuk]

Hello, everyone

I'm trying to develop netbox plugin while refering to this tutorial.

However, when step 5, I stucked because netbox rule. Therefore, I would like to add comment for this netbox rule explicitly.

problem

Add button is not shown in model list view if URL name with `_'. when refering Test the Views

ex) when model name is VLANGroupSet good: vlangroupset_add bad: vlan_group_set_add

Maybe this rule is related in /netbox/utilities/utils.py

(I cloud not find truth information, sorry)