docs: add npm install instructions to README

Author: Coding-Dev-Tools

README.md

@@ -186,3 +186,12 @@ CLI flags override config file settings.
 
 MIT — see [LICENSE](LICENSE)
 
+
+
+## Install via npm
+
+```bash
+npm install -g deadcode-cli
+```
+
+Then run: `deadcode --help`