Add documentation string to input option

src/main.rs

@@ -7,6 +7,7 @@ enum Command
 	#[structopt(about = "Verifies a logic program against a specification")]
 	VerifyProgram
 	{
+		/// ASP input program (one or multiple files)
 		#[structopt(parse(from_os_str), required(true))]
 		input: Vec<std::path::PathBuf>,
 	}