Added GetOS example

examples/core/core_get_os.c

@@ -0,0 +1,17 @@
+// Written by Rabia Alhaffar in 11/June/2020
+// Example to check current operating system used
+
+#include <raylib.h>
+
+int main(void) {
+    InitWindow(0,0,"Check OS");
+    SetTargetFPS(60);
+    while (!WindowShouldClose()) {
+        BeginDrawing();
+            ClearBackground(RAYWHITE);
+            DrawText(GetOS(),10,10,32,BLACK);
+        EndDrawing();
+    }
+    CloseWindow();
+    return 0;
+}