File README.md of Package dnsdist

Build results for dnsdist in Factory are:

![TW build results](https://br.opensuse.org/status/openSUSE:Factory/dnsdist/standard)

Build results in the devel project (server:dns) and sources at https://src.opensuse.org/dns/dnsdist

![Devel project build results](https://br.opensuse.org/status/server:dns/dnsdist)