Include URI information for `jsdom` in the README.

See #453 for an example of where this led to confusion.

README.md

@@ -29,7 +29,11 @@ This `article` object will contain the following properties:
 * `byline`: author metadata
 * `dir`: content direction
 
-If you're using Readability on the web, you will likely be able to use a `document` reference from elsewhere (e.g. fetched via XMLHttpRequest, in a same-origin `<iframe>` you have access to, etc.). Otherwise, you would need to construct such an object using a DOM parser such as [jsdom](https://github.com/tmpvar/jsdom). While this repository contains a parser of its own (`JSDOMParser`), that is restricted to reading XML-compatible markup and therefore we do not recommend it for general use.
+If you're using Readability on the web, you will likely be able to use a `document` reference from elsewhere (e.g. fetched via XMLHttpRequest, in a same-origin `<iframe>` you have access to, etc.).
+
+Otherwise, you would need to construct such an object using a DOM parser such as [jsdom](https://github.com/tmpvar/jsdom). While this repository contains a parser of its own (`JSDOMParser`), that is restricted to reading XML-compatible markup and therefore we do not recommend it for general use.
+
+If you're using `jsdom` to create a DOM object, you should ensure that the page doesn't run (page) scripts (avoid fetching remote resources etc.) as well as passing it the page's URI as the `url` property of the `options` object you pass the `JSDOM` constructor.
 
 ### Optional