Add Guide for Deploying

[cllns]

We already have a mini-guide for deploying to Heroku on the homepage, in a tab, but we should put this same information (with more explanation) into a Guide. Perhaps we should make it generic, but focus on Heroku, since it's a standard enough that we can help people.

The cause for this is that @sovetnik asked about a deploying issue in the Gitter chat. We should make it so people don't have to ask in the chat.