docs(ngBindHtml): explain that angular-sanitize.js is needed to depend on ngSanitize

Added comment. You need to include angular-sanitize.js otherwise you cant use ngSanitize!

Closes #9400

Author: tommyangelo

src/ng/directive/ngBind.js

@@ -139,7 +139,10 @@ var ngBindTemplateDirective = ['$interpolate', function($interpolate) {
  * element in a secure way.  By default, the innerHTML-ed content will be sanitized using the {@link
  * ngSanitize.$sanitize $sanitize} service.  To utilize this functionality, ensure that `$sanitize`
  * is available, for example, by including {@link ngSanitize} in your module's dependencies (not in
- * core Angular.)  You may also bypass sanitization for values you know are safe. To do so, bind to
+ * core Angular). In order to use {@link ngSanitize} in your module's dependencies, you need to
+ * include "angular-sanitize.js" in your application.
+ *
+ * You may also bypass sanitization for values you know are safe. To do so, bind to
  * an explicitly trusted value via {@link ng.$sce#trustAsHtml $sce.trustAsHtml}.  See the example
  * under {@link ng.$sce#Example Strict Contextual Escaping (SCE)}.
  *