Add a more visible warning about Apache for Window's current instability.

(Marc Slemko's wording). This is used by the IS2 configuration. It should
perhaps go into os/win32 but then it wouldn't be as obvious to people who
obtain the source tree.  Named to be consistent with README-NT.TXT
(README.NT in CVS), although both might be more correct as as *-WIN32.TXT.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@81784 13f79535-47bb-0310-9956-ffa450edef68