Added missing references

Author: javiereguiluz

components/property_info.rst

@@ -5,8 +5,8 @@
 The PropertyInfo Component
 ==========================
 
-    The PropertyInfo component extracts information about PHP class properties using
-    metadata from popular sources, like Reflection and PHP Documentation.
+    The PropertyInfo component extracts information about PHP class properties
+    using metadata from popular sources, like `Reflection`_ and `PHP Documentation`_.
 
 .. versionadded:: 2.8
     The PropertyInfo component was introduced in Symfony 2.8.
@@ -20,3 +20,7 @@ You can install the component in 2 different ways:
 * Use the official Git repository (https://github.com/symfony/property-info).
 
 For more information, see the code in the Git Repository.
+
+.. _`Reflection`: http://php.net/manual/en/book.reflection.php
+.. _`PHP Documentation`: https://www.phpdoc.org
+.. _Packagist: https://packagist.org/packages/symfony/property-info