add alt tag on tracking pixel

This came out of a discussion with a russian reader who's sometimes
using lynx to visit the site. When I tested this, the output wasn't
great, we'd see this:

    Copyleft © 2002-2016 The Anarcat CC-BY-SA. Powered by ikiwiki. Valid (X)HTML 5.

    [count?p=index&t=Anarcat]

Now we should see this:

     Copyleft © 2002-2016 The Anarcat CC-BY-SA. Powered by ikiwiki. Valid (X)HTML 5.

     tracking pixel to count visitors when Javascript is disabled