fix: update pip install command from deadcode to deadcode-cli

The package was renamed to deadcode-cli for PyPI registry availability
(commit 61c8bf2), but the README installation instructions still said
\pip install deadcode\ which would install an unrelated package.

Badges already point to deadcode-cli; the install command now matches.

Author: DevForge Engineer

README.md

@@ -16,7 +16,7 @@
 ## Installation
 
 ```bash
-pip install deadcode
+pip install deadcode-cli
 
 # Scan current project
 deadcode scan