Add extra sentence about registry to AutoDevOps popup

What does this MR do?

Temporary ugly fix until omnibus-gitlab#4690 (closed) is resolved

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content