docs: note canonical move to personal account

[zhudotexe]

Summary

As this project is no longer maintained by D&D Beyond and the MIT license allows me to continue work on it personally, I am adopting the library under my personal account. This PR adds a note to the README redirecting any other library consumers to the new canonical repository.

Checklist

PR Type

• [ ] This PR is a code change that implements a feature request.
• [ ] This PR fixes an issue.
• [ ] This PR adds a new feature that is not an open feature request.
• [x] This PR is not a code change (e.g. documentation, README, ...)

Other

• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] If code changes were made then they have been tested.
• [ ] I have updated the documentation to reflect the changes.