Sdl message box when no args provided (#3843)

* Added a message box when no arguments are passed.

* clang-fix

* clang-fix episode 2

* Output message box error to stderr instead of stdout

src/main.cpp

@@ -1,6 +1,7 @@
 // SPDX-FileCopyrightText: Copyright 2025 shadPS4 Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#include <SDL3/SDL_messagebox.h>
 #include "functional"
 #include "iostream"
 #include "string"
@@ -182,6 +183,10 @@ int main(int argc, char* argv[]) {
          }}};
 
     if (argc == 1) {
+        if (!SDL_ShowSimpleMessageBox(
+                SDL_MESSAGEBOX_INFORMATION, "shadPS4",
+                "This is a CLI application. Please use the QTLauncher for a GUI.", nullptr))
+            std::cerr << "Could not display SDL message box! Error: " << SDL_GetError() << "\n";
         int dummy = 0; // one does not simply pass 0 directly
         arg_map.at("-h")(dummy);
         return -1;