dnsmasq: update homepage link

The doc.html seems like a better choice for a homepage link than the
list of files in the containing directory listing.

Cc: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>