PuTTY website URL spelling change

[originally from svn r415]

README

@@ -27,7 +27,7 @@ alternative Makefiles themselves.
 
 The PuTTY home web site is
 
-    http://www.chiark.greenend.org.uk/~sgtatham/putty.html
+    http://www.chiark.greenend.org.uk/~sgtatham/putty/
 
 Bug reports and feature requests should be sent to
 <putty-bugs@lists.tartarus.org>. PLEASE read the section on the web