fix: panic when no sub-command is specified.

For instance, this was panicking `yr -C config.toml`.

cli/src/commands/mod.rs

@@ -55,6 +55,7 @@ pub fn cli() -> Command {
                 .long_help(help::CONFIG_FILE),
         )
         .help_template(APP_HELP_TEMPLATE)
+        .subcommand_required(true)
         .subcommands(vec![
             commands::scan(),
             commands::compile(),