Add key param to createPortal reference (#5928)

* Add key param to createPortal reference

* Update createPortal.md

* Update createPortal.md

* Update createPortal.md

---------

Co-authored-by: dan <[email protected]>

Author: mattrunyon

src/content/reference/react-dom/createPortal.md

@@ -10,7 +10,7 @@ title: createPortal
 ```js
 <div>
   <SomeComponent />
-  {createPortal(children, domNode)}
+  {createPortal(children, domNode, key?)}
 </div>
 ```
 
@@ -22,7 +22,7 @@ title: createPortal
 
 ## Reference {/*reference*/}
 
-### `createPortal(children, domNode)` {/*createportal*/}
+### `createPortal(children, domNode, key?)` {/*createportal*/}
 
 To create a portal, call `createPortal`, passing some JSX, and the DOM node where it should be rendered:
 
@@ -50,6 +50,8 @@ A portal only changes the physical placement of the DOM node. In every other way
 
 * `domNode`: Some DOM node, such as those returned by `document.getElementById()`. The node must already exist. Passing a different DOM node during an update will cause the portal content to be recreated.
 
+* **optional** `key`: A unique string or number to be used as the portal's [key.](/learn/rendering-lists/#keeping-list-items-in-order-with-key)
+
 #### Returns {/*returns*/}
 
 `createPortal` returns a React node that can be included into JSX or returned from a React component. If React encounters it in the render output, it will place the provided `children` inside the provided `domNode`.