Fix documentation of external resources fetched by default

Closes #1497.

Author: domenic

README.md

@@ -274,7 +274,7 @@ Default features are extremely important for jsdom as they lower the configurati
 
 `FetchExternalResources`
 
-- _Default_: `["script"]`
+- _Default_: `["script", "link"]`
 - _Allowed_: `["script", "frame", "iframe", "link", "img"]` or `false`
 - _Default for `jsdom.env`_: `false`