Fixed articles links

Author: javiereguiluz

cookbook/install/index.rst

@@ -5,3 +5,4 @@ Install and Upgrade
     :maxdepth: 2
 
     upgrading
+    unstable_versions

cookbook/install/inestable_versions renamed to cookbook/install/unstable_versions

@@ -107,10 +107,10 @@
   * (validation) :doc:`/cookbook/validation/custom_constraint`
   * (doctrine) :doc:`/cookbook/doctrine/file_uploads`
 
-* **Installing and Upgrading**
+* :doc:`/cookbook/install/index`
 
-  * :doc:`/cookbook/upgrading`
-  * :doc:`/cookbook/inestable_version`
+  * :doc:`/cookbook/install/upgrading`
+  * :doc:`/cookbook/install/unstable_version`
 
 * :doc:`/cookbook/logging/index`