On my Arch system, docker does not expose the tcp port by default, therefore I get the following error:

Warning: failed to get default registry endpoint from daemon
(Cannot connect to the Docker daemon at tcp://192.168.0.16:2375. Is the docker daemon running?).
Using system default: https://index.docker.io/v1/
Cannot connect to the Docker daemon at tcp://192.168.0.16:2375. Is the docker daemon running?

It took me quite some time to get the root cause of the problem. An easy fix is to enable the tcp port in the docker service configuration file /lib/systemd/system/docker.service.

Just replace the section:

[Service]
ExecStart=/usr/bin/dockerd -H fd://

by

[Service]
ExecStart=/usr/bin/dockerd -H fd:// -H tcp://0.0.0.0:2375

Make sure to reload the daemon systemctl daemon-reload and restart the docker service systemctl restart docker. This should fix the problem.

This information can also be found here.