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.

2006/README.md

@@ -16,6 +16,12 @@ This year we included most of the information included by the submitters
 in the `README.md` files (that were used to build the `index.html` web pages).
 
 
+### Historical note:
+
+The IOCCC has a website and now has a number of international mirrors.
+The primary website can be found at [www.ioccc.org](https://www.ioccc.org).
+
+
 ## Remarks on some of the entries
 
 There were some outstanding entries that did not win.  Unfortunately

2006/index.html

@@ -403,6 +403,9 @@ yours is lacking, you may need to compile using gcc instead of your
 local compiler.</p>
 <p>This year we included most of the information included by the submitters
 in the <code>README.md</code> files (that were used to build the <code>index.html</code> web pages).</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">www.ioccc.org</a>.</p>
 <h2 id="remarks-on-some-of-the-entries">Remarks on some of the entries</h2>
 <p>There were some outstanding entries that did not win. Unfortunately
 some very good entries lost because they:</p>