Fix copyright notice formatting in README.md

Author: xixu-me

README.md

@@ -4,6 +4,6 @@ This repository provides the source code of my implementation for assignments fr
 
 ## License
 
-Copyright © [Xi Xu](https://xi-xu.me). All rights reserved.
+Copyright © [Xi Xu](https://xi-xu.me).
 
 Licensed under the [GPL-3.0](LICENSE) license.