marked Silex 1.3 as being unmaintained

README.rst

 Silex, a simple Web Framework
 =============================
 
+**WARNING** Silex 1.x is not maintained anymore. Please, upgrade to Silex 2.x.
+
 Silex is a PHP micro-framework to develop websites based on `Symfony
 components`_::
 

doc/changelog.rst

 Changelog
 =========
 
-1.3.6 (2016-XX-XX)
+1.3.6 (2016-04-30)
 ------------------
 
-* n/a
+**WARNING** This is the last release of the Silex 1.x branch. Please, upgrade
+to Silex 2.x.
+
+* minor docs/tests changes
 
 1.3.5 (2016-01-06)
 ------------------

doc/intro.rst

 Introduction
 ============
 
+**WARNINIG** You are reading documentation for the Silex 1.x branch, which is
+not maintained anymore. You should upgrade to Silex 2.x.
+
 Silex is a PHP microframework. It is built on the shoulders of `Symfony`_ and
 `Pimple`_ and also inspired by `Sinatra`_.