Document user parameter in restricted function

docs/source/development/how-to-restrict-blocks.md

@@ -22,12 +22,13 @@ The function has this signature:
     block: BlockConfigBase;
     navRoot: Content;
     contentType: string;
+    user: Object
   }) => boolean;
 }
 ```
 
 Where `properties` is the current object data and `block` is the block being evaluated in `BlockChooser`.
-`navRoot` is the nearest navigation root object and `contentType` is the current content type.
+`navRoot` is the nearest navigation root object and `contentType` is the current content type. `user` is an object that represents the currently authenticated user.
 
 In the following configuration example, you can restrict a block so that it cannot be added unless the content type is `News Item` or the content item is in a specific path in the content tree (`/folder`):