Added missing note

Author: mitsuhiko

README

@@ -44,6 +44,11 @@
 
          $ virtualenv-tools --update-path /srv/your-application/<hash>
 
+       To also update the Python executable in the virtualenv to the
+       system one you can reinitialize it in one go:
+
+         $ virtualenv-tools --reinitialize /srv/your-application/<hash>
+
 
      Compile once, deploy whereever.  Virtualenvs are completely self
      contained.  In order to switch the current version all you need to