Add GC limitation note in README.md

Author: kateinoigakukun

packages/npm-packages/ruby-head-wasm-wasi/README.md

@@ -85,6 +85,34 @@ See [the example project](https://github.com/ruby/ruby.wasm/tree/main/packages/n
 </html>
 ```
 
+
+## GC limitation with JavaScript interoperability
+
+Since JavaScript's GC system and Ruby's GC system are separated and not cooperative, they cannot collect cyclic references between JavaScript and Ruby objects.
+
+The following code will cause a memory leak:
+
+```javascript
+class JNode {
+  setRNode(rnode) {
+    this.rnode = rnode;
+  }
+}
+jnode = new JNode();
+
+rnode = vm.eval(`
+class RNode
+  def set_jnode(jnode)
+    @jnode = jnode
+  end
+end
+RNode.new
+`)
+
+rnode.call("set_jnode", vm.wrap(jnode))
+jnode.setRNode(rnode);
+```
+
 <!-- The APIs section was generated by `npx documentation readme ./dist/index.esm.js --section=APIs` -->
 
 ## APIs