Freezing: clarify how it affects Python security updates

Author: tartley

docs/shipping/freezing.rst

@@ -16,8 +16,9 @@ Windows, and even on many Linux distributions and OSX versions, the right
 version of Python will not already be installed.
 
 One disadvantage is that it will bloat your distribution by about 2Mb.
-Another problem is that your application, once downloaded by a user, will
-not receive any security updates to the version of Python it uses.
+Another problem is that your application will not receive any security updates
+to the version of Python it uses unless you freeze a new version and get
+users to download it.
 
 Alternatives to Freezing
 ------------------------