Add note about validating webhooks

README.md

@@ -10,6 +10,12 @@
 Use Twilio to receive SMS and MMS messages. For a step-by-step tutorial see the
 <a href="https://www.twilio.com/docs/guides/receive-and-download-images-incoming-mms-messages-ruby-rails">Twilio docs</a>.
 
+## Note: protect your webhooks
+
+Twilio supports HTTP Basic and Digest Authentication. Authentication allows you to password protect your TwiML URLs on your web server so that only you and Twilio can access them.
+
+Learn more about HTTP authentication [here](https://www.twilio.com/docs/usage/security#http-authentication), which includes sample code you can use to secure your web application by validating incoming Twilio requests.
+
 ## Local development
 
 This project is built using the [Ruby on Rails](http://rubyonrails.org/) web framework.