dnscrypt-proxy service: additional hardening

Run the daemon with private /home and /run/user to
prevent it from enumerating users on the system.

nixos/modules/services/networking/dnscrypt-proxy.nix

@@ -204,6 +204,7 @@ in
 
         PrivateTmp = true;
         PrivateDevices = true;
+        ProtectHome = true;
       };
     };
   };