Add new contributor to CREDITS.md

[krm-shrftdnv]

Changes proposed in this pull request:

Add new contributor https://github.com/FreshRSS/FreshRSS/pulls?q=is:pr+author:krm-shrftdnv

Pull request checklist:

• [x] clear commit messages
• [ ] code manually tested
• [ ] unit tests written (optional if too hard)
• [ ] documentation updated

Additional information can be found in the documentation.