DEPLOY.md needs a few more tweaks before it can be setup on Heroku

When I was deploying this app, I found out that there were a few pieces missing before I could get everything up and running. The main thing was that emails were not being sent out, and this happens even on the Kandan demo Heroku app:

![screen shot 2014-04-02 at 2 14 42 am](https://cloud.githubusercontent.com/assets/463175/2587905/295ebc84-ba2e-11e3-8bb2-b1464207cc94.png)

To fix these issues, three things need to happen:

* production.rb needs to have a config setting for config.action_mailer.default_url_options = { :host => "whatever" }
* the Heroku app needs a mail service add-on for it (I use Sendgrid in my example)
* Those email add-on options need to be added to production.rb for emails to go out.