docs(guide/Working With CSS): add doc for ng-isolate-scope

Author: Justin Walsh

docs/content/guide/css-styling.ngdoc

@@ -12,6 +12,10 @@ Angular sets these CSS classes. It is up to your application to provide useful s
   - **Usage:** angular applies this class to any element for which a new {@link $rootScope scope}
     is defined. (see {@link guide/scope scope} guide for more information about scopes)
 
+* `ng-isolate-scope`
+  - **Usage:** angular applies this class to any element for which a new 
+    {@link guide/directive#isolating-the-scope-of-a-directive isolate scope} is defined. 
+
 * `ng-binding`
   - **Usage:** angular applies this class to any element that is attached to a data binding, via `ng-bind` or
     `{{}}` curly braces, for example. (see {@link guide/databinding databinding} guide)