Add documentation for templated webhooks

Add documentation for templated webhooks, with examples to work with Twilio's api and with Jira On demand

![screen shot 2014-07-29 at 5 38 01 pm](https://cloud.githubusercontent.com/assets/3354626/3742367/a65b0b7e-1768-11e4-872c-4c0746a5b1b8.png)