Update registry.json

[MladenLm]

Added RUMOR SPO to the list

Commitment

By submitting this PR I agree that I will fight for the full decentralization of Cardano by only running a single pool and reporting members that are breaking the rules by running multiple pools.

PR Checklist

I have:

• Added a telegram handle of an individual and not that of a group or channel.
• Added a social media account with activity.
• Removed any @ characters from Telegram, Instagram or Twitter handles.
• Provided my operator name as my real full name, my real first name, or I have left that field blank.
• Included all social media fields in the PR even if they are blank (this will fail validation if not done).