add raygui example

main.c

@@ -1,7 +1,40 @@
 #include <stdio.h>
 
+#include "raylib.h"
+#define RAYGUI_IMPLEMENTATION
+#include "raygui.h"
+
 int main(void) {
-    printf("Hello\n");
+    InitWindow(400, 200, "App");
+    SetTargetFPS(60);
+
+    bool showMessageBox = false;
+
+    while (!WindowShouldClose()) {
+        BeginDrawing();
+        ClearBackground(GetColor(GuiGetStyle(DEFAULT, BACKGROUND_COLOR)));
+
+        if (GuiButton((Rectangle){24, 24, 120, 30}, "#191Show Message")) {
+            showMessageBox = true;
+        }
+
+        if (showMessageBox) {
+            int result = GuiMessageBox(
+                (Rectangle){85, 70, 250, 100},
+                "#191Message Box",
+                "Hi! This is a message!",
+                "Nice;Cool"
+            );
+
+            if (result >= 0) {
+                showMessageBox = false;
+            }
+        }
+
+        EndDrawing();
+    }
+
+    CloseWindow();
 
     return 0;
 }