link to mailing lists webpage

(another test of git server migration :)

README

@@ -8,3 +8,6 @@ The developers website is at http://kea.isc.org/
 
 Limitations and known issues with this DHCP release can be found
 at http://kea.isc.org/wiki/KeaKnownIssues
+
+The Kea mailing lists are available via
+https://lists.isc.org/