Add description for unowned parts in network ownership

[Ticko-Grey]

Changes

The network ownership article does not document what black debug visualization means, I have added documentation for that here.

https://devforum.roblox.com/t/what-is-black-network-ownership/2872112

Checks

By submitting your pull request for review, you agree to the following:

• [ x ] This contribution was created in whole or in part by me, and I have the right to submit it under the terms of this repository's open source licenses.
• [ x ] I understand and agree that this contribution and a record of it are public, maintained indefinitely, and may be redistributed under the terms of this repository's open source licenses.
• [ x ] To the best of my knowledge, all proposed changes are accurate.

[github-actions]

Hi @Ticko-Grey, thanks so much for helping improve the Roblox creator documentation! Our technical writing team will review your pull request soon. In the meantime, please ensure you've read through the README.md, contribution guidelines, and style recommendations.