add install-digital-ocean
edits to digital ocean guide for clarity
another pass on digital ocean guide
we need a bit more top-margin on h1,h2,h3
improve first two images in digital ocean guide
that ssh-add command is not required
no needless two line commands please, WTF
nano clarification
omit needless words
clarify guide details
clarify guide details
email deliverability test copy update
header updates on DO guide
Update INSTALL-digital-ocean.md

Why not use the docker install script? It has checks to make sure things are installed correctly. It could also be done via curl: 'curl -sL https://get.docker.io/ | sh'.

There's also https://get.docker.io/ubuntu/ as well, which has less checks.

Finally, should there be steps to set up an additional user and disable root login? Seems a little insecure.
Left command in quotes.
One last thing...

it's a little early here... sorry!
Merge pull request #1999 from trident523/patch-2

Update INSTALL-digital-ocean.md
clean up guide, add mailgun/mailjet opt
guide tweak
omit needless words