Story: as a user, I want to send an SMS to a Twilio number and receive a list of commands available in an SMS interface

[kwhinnery]

For this system, we intended to have users text in to a Twilio number to be able to subscribe for updates on open data sources they care about. The first step will be responding to an SMS and displaying a menu of commands they can text in to interact with the system. Some placeholder commands might be:

• subscribe (subscribe for a particular kind of notification)
• list (see what things I can subscribe to)
• help and anything else (print the menu of options)

Acceptance criteria

• Modify the placeholder webhook to process the incoming SMS for different keywords
• For now, respond only with a list of available commands that the user could theoretically input into the system
• Modify (and add new potentially) integration tests for the endpoint, and any helpers you might need to add