Add DigitalOcean deployment guide

[tanner0101]

Adds two guides:

• Setup Ubuntu VM via DigitalOcean
• Deploy example app on Ubuntu VM

Future direction

• Nginx for serving on port 80
• Setup CentOS (and others) via DigitalOcean
• Deploy example app on CentOS (and other) VMs
• Add Docker with Ubuntu VM

[tomerd]

this is great @tanner0101 some notes/ideas about security best practices

[tanner0101]

@tomerd updated.