Add README to the logutil package

What does this MR do?

Add a README.md to the logutil package. The README allows us to link to it for usage examples from the GitLab docs. See gitlab-org/gitlab!34356 (merged) for an example of cross linking.

What are the relevant issue numbers?

gitlab-org/gitlab#10880 (closed)

Does this MR meet the acceptance criteria?

• [-] Changelog entry added
• [-] Documentation created/updated for GitLab EE, if necessary
• [-] Documentation created/updated for this project, if necessary
• [-] Documentation reviewed by technical writer or follow-up review issue created
• [-] Tests added for this feature/bug
• [-] Job definition updated, if necessary
  • [-] Auto-DevOps template
  • [-] Job definition example
  • [-] CI Templates
• [-] Conforms to the code review guidelines
• [-] Conforms to the Go guidelines
• [-] Security reports checked/validated by reviewer