add checkmark to the narbar of all constructed HTML

We added a checkmark all narbar's that has the make effect of
clicking on the **Nu HTML check this web page** link at the very
bottom.  This makes it much more convenient when one needs
to quickly check the HTML of a number of web pages.

Run `make www` to perform the above.

1991/brnstnd/sorta.README.html

@@ -122,6 +122,7 @@
 
 <div class="navbar">
   <a class="Left" href="index.html">&uarr; jump to index.html &uarr;</a>
+  <a class="Right" href="https://validator.w3.org/nu/?doc=#">&#x2713;</a>
 </div>
 
 <!-- END: this line ends content from: inc/navbar.up2index.html -->