Update README.md

Author: umpire274

README.md

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 **rbackup** is a fast, cross-platform, and multithreaded command-line utility written in Rust for performing incremental backups of directories. It is inspired by tools like `rsync` and `robocopy`, but designed with simplicity, portability, and localization in mind.
 
+![CI](https://github.com/umpire274/rbackup/actions/workflows/ci.yml/badge.svg)
 ![MIT License](https://img.shields.io/badge/license-MIT-green.svg)
 ![Platform](https://img.shields.io/badge/platform-Windows%20%7C%20Linux%20%7C%20macOS-blue)
 ![Version](https://img.shields.io/badge/version-0.2.0-orange)