add note about zsh completion support

--HG--
extra : convert_revision : svn%3A98f53aa3-d424-0410-b225-a548b0275c4d/Projects/virtualenvwrapper/trunk%401851

Author: dhellmann

README

@@ -70,6 +70,10 @@ For more details, refer to the column I wrote for the May 2008 issue of Python M
 Updates
 =======
 
+1.6
+
+  - Add completion support for zsh, courtesy of Ted Leung.
+
 1.5
 
   - Fix some issues with spaces in directory or env names.  They still don't really work with virtualenv, though.