Note about selector class import

This is the salient point of this code compared to the last example.  We have a selector now and this is how we use it.  Especially since the user has just come from the shell where the pre-instantiated selector is taken for granted.

docs/intro/tutorial.rst

@@ -363,6 +363,8 @@ Let's add this code to our spider::
                desc = site.xpath('text()').extract()
                print title, link, desc
 
+Notice we import our Selector class from scrapy.selector and instantiate a 
+new Selector object.  We can now specify our XPaths just as we did in the shell.
 Now try crawling the dmoz.org domain again and you'll see sites being printed
 in your output, run::