Add missing import

When copy/pasting the displayed code sample my IDE tells me to import "Tokens" so I suggest that it's added to the docs as well :)

Author: BatJan

15/umbraco-cms/reference/umbraco-flavored-markdown.md

@@ -127,6 +127,7 @@ If you wish to develop your own custom UFM component, you can use the `ufmCompon
 The corresponding JavaScript/TypeScript API would contain a method to render the custom label/markup.
 
 ```js
+import { Tokens } from '@umbraco-cms/backoffice/external/marked';
 import { UmbUfmComponentBase } from '@umbraco-cms/backoffice/ufm';
 
 export class MyCustomUfmComponentApi extends UmbUfmComponentBase {