Fix links of how-to-bugfix.md to how-to-help.md

I neglected to do this when I renamed the file.

index.html

@@ -56,7 +56,7 @@ then consider making pull requests against the
 <A HREF="years.html">Winning entries</A>
 <BR><BR>
 <A HREF="bugs.md">Known Bugs &amp; (Mis)features</A> |
-<A HREF="how-to-bugfix.md">How to fix an IOCCC winner</A> |
+<A HREF="how-to-help.md">How to fix an IOCCC winner</A> |
 <A HREF="thanks-for-fixes.md">Thanks for the fixes</A> |
 <A HREF="www-history.md">A bit of web site history</A>
 </CENTER>