Add release notes for cvmfs-2.13.3

Author: vvolkl

conf.py

@@ -63,7 +63,7 @@
 # The short X.Y version.
 version = u'2.13'
 # The full version, including alpha/beta/rc tags.
-release = u'2.13.2'
+release = u'2.13.3'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.