Add mirror references back as historical note

Instead of having the mirror note in the YYYY/index.html files
completely removed it is back but as a historical note.

2004/index.html

@@ -401,6 +401,9 @@ You may then wish to look at the Author’s remarks for even more details.</p>
 <p>Some ANSI C compilers are not quite as good as they should be. If
 yours is lacking, you may need to compile using <code>gcc</code> instead of your
 local compiler.</p>
+<h3 id="historical-note">Historical note:</h3>
+<p>The IOCCC has a website and now has a number of international mirrors.
+The primary website can be found at <a href="https://www.ioccc.org/" class="uri">https://www.ioccc.org/</a>.</p>
 <h2 id="remarks-on-some-of-the-entries">Remarks on some of the entries</h2>
 <p>We believe you will be impressed with this year’s winning entries. The <a href="gavin/index.html">Best of
 Show</a> is a fine example of obfuscation. But don’t ignore the