Add Angular to Index (#2976)

free-programming-books-pt_BR.md

@@ -11,6 +11,7 @@
 * [HTML / CSS](#html--css)
 * [Java](#java)
 * [JavaScript](#javascript)
+  * [Angular](#angular)
   * [Angular.js](#angularjs)
   * [Backbone.js](#backbonejs)
   * [Ember.js](emberjs)