Modifies welcome message sent to users who use the form to say:
Hi there! Reply to this message with your EBT card number and we'll check your balance for you. For more info, text ABOUT.
Lets a user text in ABOUT (or about, or About) and receive the following message:
This is a free text service provided by non-profit Code for America for checking your EBT balance (standard rates apply). For more info go to www.c4a.me/balance
Closes #272