Display help when there is no subcommand

src/main.zig

@@ -69,5 +69,10 @@ pub fn main() !void {
 
         try @import("./server/main.zig").main(gpa, info);
         return;
+    } else if (matches.subcommandMatches("pub")) |_| {
+        std.debug.print("Unimplemented\n", .{});
+        return;
     }
+
+    try app.displayHelp(io);
 }