add CocoIndex to repositories.toml

[badmonster0]

trafficstars

ℹ️ Repository information

repo: https://github.com/cocoindex-io/cocoindex

docs: https://cocoindex.io/

The repository has:

• [x] At least three issues with the good first issue label.
• [x] At least 10 contributors.
• [x] Detailed setup instructions for the project.
• [x] CONTRIBUTING.md
• [x] Actively maintained.