Explain how to restore a wholly stubbed object

I'm proposing this change based on [this issue](#1553).

Should this explanation be more specific? The only way I was able to access this method was by importing it directly with
```js
import restore from 'sinon/lib/sinon/util/core/restore.js'
```
Is there a more direct way to use it?

docs/_releases/latest/stubs.md

@@ -86,7 +86,7 @@ A [codemod is available](https://github.com/hurrymaplelad/sinon-codemod) to upgr
 
 #### `var stub = sinon.stub(obj);`
 
-Stubs all the object's methods.
+Stubs all the object's methods. Use the `restore` utility to restore an object stubbed this way.
 
 Note that it's usually better practice to stub individual methods, particularly on objects that you don't understand or control all the methods for (e.g. library dependencies).