Fix completions for utils and add description

src/app.rs

@@ -12,7 +12,7 @@ const MAIN_C: &str = include_str!("templates/main.c");
 const GITIGNORE: &str = "target/";
 
 #[derive(clap::Parser)]
-#[clap(version)]
+#[clap(version, about)]
 pub struct App {
     #[clap(subcommand)]
     command: Subcommand,
@@ -54,6 +54,7 @@ enum UtilSubcommand {
     /// Generate shell completions
     Completions {
         /// The shell to generate completions for
+        #[arg(value_enum, long, short)]
         shell: ShellCompletions,
     },
 }