Add more instructions about headless systems.

[AndrewSouthpaw]

Hello! I stumbled a fair bit trying to get this running on DigitalOcean. The instructions were great, but I fell into a couple easy mistakes because of my unfamiliarity with Linux and remote systems.

I hope these additions would be helpful to someone else! Just trying to give back to the community. 😄

Great project!

[AndrewSouthpaw]

Thanks for the feedback! Updated.