adding git stage support

Author: perryqh

tests/git_stage_test.rs

@@ -41,4 +41,4 @@ where
     assert!(run_config.codeowners_file_path.exists(), "CODEOWNERS file was not created");
     let staged = is_file_staged(&run_config.project_root, CODEOWNERS_REL);
     assert_eq!(staged, expected_staged, "unexpected staged state for CODEOWNERS");
-}
+}