docs: Add reference link for V8 engine resource management

Author: HowieHz

src/main/java/top/howiehz/halo/plugin/extra/api/service/js/runtime/engine/impl/V8EnginePoolServiceImpl.java

@@ -84,6 +84,7 @@ public void afterPropertiesSet() throws Exception {
      */
     @Override
     public void destroy() throws Exception {
+        // https://www.caoccao.com/Javet/reference/resource_management/load_and_unload.html
         if (enginePool != null) {
             try {
                 enginePool.close();