Add help message

build_system/src/main.rs

@@ -9,13 +9,19 @@
 macro_rules! arg_error {
     ($($err:tt)*) => {{
         eprintln!($($err)*);
+        eprintln!();
         usage();
         std::process::exit(1);
     }};
 }
 
 fn usage() {
-    // println!("{}", include_str!("usage.txt"));
+    println!("\
+Available commands for build_system:
+
+    prepare  : Run prepare command
+    build    : Run build command
+    --help   : Show this message");
 }
 
 pub enum Command {
@@ -31,6 +37,10 @@ fn main() {
     let command = match env::args().nth(1).as_deref() {
         Some("prepare") => Command::Prepare,
         Some("build") => Command::Build,
+        Some("--help") => {
+            usage();
+            process::exit(0);
+        }
         Some(flag) if flag.starts_with('-') => arg_error!("Expected command found flag {}", flag),
         Some(command) => arg_error!("Unknown command {}", command),
         None => {