Adding ldns builds additional plugins for rewriting DNS queries,
such as blocking and forwarding.
For example, to use a custom domain blocklist, you can do
```nix
let
myBlockListFile = writeText "blocked-domains" ''
*.example.com
'';
in
{
services.dnscrypt-proxy.extraArgs = [
"-X libdcplugin_example_ldns_blocking.so,--domains=${myBlockListFile}"
];
}
```