keep a list of implemented features

https://github.com/statnett/KGraphPy/blob/main/ReadMe.adoc is very wide in scope.
Please maintain a more concrete file (or section) that describes all implemented features.

Eg https://github.com/statnett/KGraphPy/blob/main/cim_plugin/cimxml.py
- does it emit named graphs?
- what output formats does it support?
- does it support DifferentialModel? (not yet)