Add CleanClip

[s1ntoneli]

0. [x] I have read the Contribution Guidelines
1. [x] Project URL: https://cleanclip.cc
2. [x] Why should this project be added: CleanClip is a super clean clipboard manager app. It can help us automatically record the copy history of the clipboard, avoiding important content being overwritten. I think CleanClip will greatly help us in our daily work.
3. [x] End all descriptions with a full stop/period
4. [x] Entry is ordered alphabetically
5. [x] Appropriate icon(s) added if applicable (OSS, freeware)

[s1ntoneli]

Hey, I want to apologize to @herrbischoff. In the previous PR, I carelessly didn't notice the colon after "Project URL" and thought that adding the URL in the README would be enough. However, I assure you that I have read the contribution guidelines multiple times to ensure that I did not violate any of the conventions. I apologize for wasting your time.