Add RewriteBar

[m91michel]

0. I have read the Contribution Guidelines
1. Project URL: https://rewritebar.com
2. Why should this project be added: RewriteBar is a small (6 MB) menubar app that lets you perform text transformations with the help of AI. You can select text in any application and trigger a transformation. It uses OpenAI to execute transformations such as text improvements, translations, changing the tone, or whatever you can imagine. It's super helpful for any writing task. It's a native macOS app written in Swift and SwiftUI, and it has no clunky UI or anything like that. It is merely a menubar app.
3. End all descriptions with a full stop/period
4. Entry is ordered alphabetically
5. Appropriate icon(s) added if applicable (OSS, freeware)

[m91michel]

I was unsure if it belongs to Productivity or Utilities. I could change that if you like :)