1. Since btcd is not public repository still, copy/checkout
https://github.com/daglabs/btcd into vendor/github.com/daglabs/btcd before
running "docker build".

2. To build docker image invoke following command from dnsseeder directory:
         docker build -t dnsseeder -f ./docker/Dockerfile .

3. To run
         sudo docker run -u root -p 53:53/udp dnsseeder