Added links to Looking Ahead pointing to docs mentioned

docs/guide/start-looking-ahead.md

@@ -9,19 +9,19 @@ code automatically. Using Gii for code generation turns the bulk of your Web dev
 This section will summarize the Yii resources available to help you be more productive when using the framework.
 
 * Documentation
-    - The Definitive Guide:
+    - [The Definitive Guide](http://www.yiiframework.com/doc-2.0/guide-README.html):
       As the name indicates, the guide precisely defines how Yii should work and provides general guidance
       about using Yii. It is the single most important Yii tutorial, and one that you should read 
       before writing any Yii code.
-    - The Class Reference:
+    - [The Class Reference](http://www.yiiframework.com/doc-2.0/index.html):
       This specifies the usage of every class provided by Yii. It should be mainly used when you are writing
       code and want to understand the usage of a particular class, method, property. Usage of the class reference is best only after a contextual understanding of the entire framework.
-    - The Wiki Articles:
+    - [The Wiki Articles](http://www.yiiframework.com/wiki/?tag=yii2):
       The wiki articles are written by Yii users based on their own experiences. Most of them are written
       like cookbook recipes, and show how to solve particular problems using Yii. While the quality of these
       articles may not be as good as the Definitive Guide, they are useful in that they cover broader topics
       and can often provide ready-to-use solutions.
-    - Books
+    - [Books](http://www.yiiframework.com/doc/)
 * [Extensions](http://www.yiiframework.com/extensions/):
   Yii boasts a library of thousands of user-contributed extensions that can be easily plugged into your applications, thereby making your application development even faster and easier.
 * Community