[Add App] Rainbow

[SeeDborg]

Preflight Checklist

• [x] I have read the Contributing Guidelines for this project.
• [x] I agree to follow the Code of Conduct that this project adheres to.
• [x] I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Problem Description

Hello, Would it be possible to add Rainbow from https://www.openrainbow.com ? Thanks for the wonderful software :)

Proposed Solution

Use Rainbow in Ferdium

Alternatives Considered

There is an online version on : https://web.openrainbow.net/

Additional Information

No response