improve error message

Author: magiclen

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "xcompress"
-version = "0.11.4"
+version = "0.11.5"
 authors = ["Magic Len <[email protected]>"]
 edition = "2018"
 repository = "https://github.com/magiclen/xcompress"

src/main.rs

@@ -133,7 +133,7 @@ fn main() -> Result<(), Box<dyn Error>> {
 
         handle_archive(&matches, &input_paths, output_path, best_compression, split)
     } else {
-        unimplemented!()
+        Err("Please input a subcommand. Use `help` to see how to use this program.".into())
     }
 }