coin3d: update paper link

coin3d/index.html

@@ -179,7 +179,7 @@ <h1 class="text-primary font-sans text-3xl xl:text-5xl text-center dark:text-whi
           </ul>
         </div>
         <div class="w-full flex flex-wrap justify-center items-center gap-5">
-          <a href="index.html" target="_blank"
+          <a href="https://raw.githubusercontent.com/wqdong8/open_access_assets/main/coin3d/coin3d.pdf" target="_blank"
             class="flex flex-row items-center space-x-2 rounded-full pl-2 pr-3 py-1 bg-black bg-opacity-70 hover:bg-opacity-80 transition duration-200 ease-in-out cursor-pointer dark:bg-white dark:bg-opacity-10 dark:hover:bg-opacity-20">
             <svg width="24" height="24" viewBox="0 0 24 24" class="fill-white w-5 h-5">
               <!-- xmlns="http://www.w3.org/2000/svg" -->