build: add ci

Author: harryplusplus

.github/workflows/build.yml renamed to .github/workflows/CI.yml

@@ -2,6 +2,11 @@
 
 ![logo](docs/images/logo.jpg)
 
+[![Build Status][actions-badge]][actions-url]
+
+[actions-badge]: https://github.com/oneofthezombies/kill-tree/workflows/CI/badge.svg
+[actions-url]: https://github.com/oneofthezombies/kill-tree/actions?query=workflow?CI+branch=main
+
 A library and CLI tool that kills all of target process and its children recursively not depending on the other commands such as `kill`, `ps`, `pgrep`, `taskkill` or `wmic`.  
 This is written in Rust and powered by [Tokio](https://github.com/tokio-rs/tokio).  
 This project is inspired by [node-tree-kill](https://github.com/pkrumins/node-tree-kill).  Thank you. 🤟