Add a link to the Macintosh Module Reference here, too.

Doc/html/index.html

@@ -12,6 +12,9 @@
 
 <LI><A HREF="lib/lib.html">Library Reference</A> (keep this under your pillow)
 
+<LI><A HREF="mac/mac.html">Macintosh Module Reference</A> (this too,
+     if you use a Macintosh)
+
 <LI><A HREF="ref/ref.html">Language Reference</A> (for language lawyers)
 
 <LI><A HREF="ext/ext.html">Extending and Embedding</A> (tutorial for