Add CleanClip

[s1ntoneli]

0. I have read the Contribution Guidelines
1. Project URL: https://cleanclip.cc
2. 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. End all descriptions with a full stop/period
4. Entry is ordered alphabetically
5. 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.