Add native Command Book app to the Developers category

[mikeckennedy]

0. I have read the Contribution Guidelines
1. Project URL: https://commandbookapp.com
2. Why should this project be added: It is a new native Swift/SwiftUI app build for developers and other people who can use some automation or use the terminal frequently.
3. End all descriptions with a full stop/period
4. Entry is ordered alphabetically
5. Appropriate icon(s) added if applicable (OSS, freeware)

Thank you!