[CSS21] error in counters example

It was pointed out in [1] that there is an error in the first example in
section 12.4 [2].  The simplest fix is to add a style rule to the
example:

  body { counter-reset: chapter; }   /* create a chapter counter scope */

so that the implicit counter creation rules don't create a separate
counter for each header.

-David

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=288946
[2] http://www.w3.org/TR/2005/WD-CSS21-20050613/generate.html#counters

-- 
L. David Baron                                <URL: http://dbaron.org/ >
          Technical Lead, Layout & CSS, The Mozilla Foundation