Clarify difference, usage and schema of `networks.json` and `networks.local.json`

[MbBrainz]

Its not entrirely clear to me from the documentation which values i need to edit in the networks.json or which i can overwrite in the networks.local.json. Would be nice if someone would update the readme to clarify this part

Specifically unclear to me:

• When im running this service for my validator, should i change the "ownerAddress" in networks.json or should i change that in the local version.
• What values are costumisable? in the networks configs
• What values are strictly required in both networks configs