fix internal links in entry index.html from 1984 thru 2012

2001/kev/index.html

@@ -229,7 +229,7 @@ getting the ball past your opponent’s paddle. It’s pretty fun! :)</p>
 the name of the machine running the server, e.g.</p>
 <pre><code>    ./kev localhost</code></pre>
 <p>Make sure that the terminals on both ends are the same size. Also, the TCP port
-number (by default 5455) specified in the <a href="Makefile">Makefile</a> mustn’t be
+number (by default 5455) specified in the <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2001/kev/Makefile">Makefile</a> mustn’t be
 blocked by a firewall.</p>
 <p>Here’s a good quick example to see it in action on your own
 machine, assuming you have <code>Xwindows</code>:</p>