better mimick dwm on version, also tested

src/main.rs

@@ -31,7 +31,7 @@ fn main() -> anyhow::Result<()> {
         if arg != "-v" {
             return Err(anyhow!("usage: rswm [-v]"));
         } else {
-            println!(env!("CARGO_PKG_VERSION")); // TODO: test this
+            println!("rswm-{}", env!("CARGO_PKG_VERSION"));
             return Ok(());
         }
     }