docs(guide): add SEO4Ajax to the SEO tools list

Closes angular#4748

Author: G Lormeau

docs/content/guide/index.ngdoc

@@ -108,7 +108,7 @@ This is a short list of libraries with specific support and documentation for wo
 
 * **Tracking:** [Angularyitcs (Google Analytics)](http://ngmodules.org/modules/angularytics), [Logging Client-Side Errors](http://www.bennadel.com/blog/2542-Logging-Client-Side-Errors-With-AngularJS-And-Stacktrace-js.htm)
 
-* **SEO:** [By hand](http://www.yearofmoo.com/2012/11/angularjs-and-seo.html), [prerender.io](http://prerender.io/), [Brombone](http://www.brombone.com/), [SEO.js](http://getseojs.com/)
+* **SEO:** [By hand](http://www.yearofmoo.com/2012/11/angularjs-and-seo.html), [prerender.io](http://prerender.io/), [Brombone](http://www.brombone.com/), [SEO.js](http://getseojs.com/), [SEO4Ajax](http://www.seo4ajax.com/)
 
 ### Server-Specific