docs(external-resources): add new book link and alphabetize

Closes #15421

Author: packtpartner

Diff for: docs/content/guide/external-resources.ngdoc

@@ -117,16 +117,17 @@ You can find a larger list of Angular external libraries at [ngmodules.org](http
 ## General Learning Resources
 
 ### Books
-* [AngularJS: Up and Running](http://www.amazon.com/AngularJS-Running-Enhanced-Productivity-Structured/dp/1491901942) by Brad Green and Shyam Seshadri
-* [Mastering Web App Development](http://www.amazon.com/Mastering-Web-Application-Development-AngularJS/dp/1782161821) by Pawel Kozlowski and Pete Bacon Darwin
 * [AngularJS Directives](http://www.amazon.com/AngularJS-Directives-Alex-Vanston/dp/1783280336) by Alex Vanston
-* [Recipes With AngularJS](http://www.amazon.co.uk/Recipes-Angular-js-Frederik-Dietz-ebook/dp/B00DK95V48) by Frederik Dietz
-* [Developing an AngularJS Edge](http://www.amazon.com/Developing-AngularJS-Edge-Christopher-Hiller-ebook/dp/B00CJLFF8K) by Christopher Hiller
-* [ng-book: The Complete Book on AngularJS](http://ng-book.com/) by Ari Lerner
+* [AngularJS Essentials (Free eBook)](https://www.packtpub.com/packt/free-ebook/angularjs-essentials) by Rodrigo Branas
 * [AngularJS : Novice to Ninja](http://www.amazon.in/AngularJS-Novice-Ninja-Sandeep-Panda/dp/0992279453) by Sandeep Panda
 * [AngularJS UI Development](http://www.amazon.com/AngularJS-UI-Development-Amit-Ghart-ebook/dp/B00OXVAK7A) by Amit Gharat and Matthias Nehlsen
-* [Responsive Web Design with AngularJS](http://www.amazon.com/Responsive-Design-AngularJS-Sandeep-Kumar/dp/178439842X) by Sandeep Kumar Patel
+* [AngularJS: Up and Running](http://www.amazon.com/AngularJS-Running-Enhanced-Productivity-Structured/dp/1491901942) by Brad Green and Shyam Seshadri
+* [Developing an AngularJS Edge](http://www.amazon.com/Developing-AngularJS-Edge-Christopher-Hiller-ebook/dp/B00CJLFF8K) by Christopher Hiller
+* [Mastering Web App Development](http://www.amazon.com/Mastering-Web-Application-Development-AngularJS/dp/1782161821) by Pawel Kozlowski and Pete Bacon Darwin
+* [ng-book: The Complete Book on AngularJS](http://ng-book.com/) by Ari Lerner
 * [Professional AngularJS](http://www.amazon.com/Professional-AngularJS-Valeri-Karpov/dp/1118832078/)
+* [Recipes With AngularJS](http://www.amazon.co.uk/Recipes-Angular-js-Frederik-Dietz-ebook/dp/B00DK95V48) by Frederik Dietz
+* [Responsive Web Design with AngularJS](http://www.amazon.com/Responsive-Design-AngularJS-Sandeep-Kumar/dp/178439842X) by Sandeep Kumar Patel
 
 ### Videos:
 * [egghead.io](http://egghead.io/)