Fixed dangling modifier in docs/settings.txt

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4491 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/settings.txt

@@ -829,7 +829,7 @@ running in the correct environment.
 
 .. note::
     Django cannot reliably use alternate time zones in a Windows environment.
-    When running Django on Windows this variable must be set to match the
+    If you're running Django on Windows, this variable must be set to match the
     system timezone.
 
 URL_VALIDATOR_USER_AGENT