Update git rules (5.5 is stable, 5.3 sec only)

Author: johannes

README.GIT-RULES

@@ -45,14 +45,17 @@ Currently we have the following branches in use::
 
   master    The active development branch. 
 
-  PHP-5.4   Is used to release the PHP 5.4.x series. It still allows for
-            larger enhancements.
+  PHP-5.5   Is used to release the PHP 5.5.x series. This is a current
+            stable version and is open for bugfixes only.
 
-  PHP-5.3   Is used to release the PHP 5.3.x series. This is current 
+  PHP-5.4   Is used to release the PHP 5.4.x series. This is a current
             stable version and is open for bugfixes only.
 
-  PHP-5.2   Is used to release the PHP 5.2.x series. It is closed for 
-            changes now.
+  PHP-5.3   Is used to release the PHP 5.3.x series. This is currently 
+            in extended support and open forsecurity fixes only. Triaged
+            via [email protected]
+
+  PHP-5.2   This branch is closed.
 
   PHP-5.1   This branch is closed.