message: Improve docs : add a section about Messaging type in readme-facebook.md
diff: @@ -21,6 +21,7 @@ Table of Contents
  * [Silent and No Notifications](#silent-and-no-notifications)
  * [Messenger code API](#messenger-code-api)
  * [Attachment upload API](#attachment-upload-api)
  +* [Messaging type](#messaging-type)
  * [Running Botkit with an Express server](#use-botkit-for-facebook-messenger-with-an-express-web-server)
  ## Getting Started
  @@ -571,6 +572,31 @@ bot.reply(message, taggedMessage);
  ```
  +## Messaging type
  +
  +You can identify the purpose of the message being sent to Facebook by adding `messaging_type: <MESSAGING_TYPE>` property when sending the message :
  +
  +```javascript
  +var messageToSend = {
  + "text": "Hello Botkit !",
  + "messaging_type": "RESPONSE"
  +};
  +bot.reply(message, messageToSend);
  +```
  +
  +This is a more explicit way to ensure bots are complying with Facebook policies for specific messaging types and respecting people's preferences.
  +
  +The following values for 'messaging_type' are supported :
  +
  +| Messaging Type | Description
  +|-----|---
  +| RESPONSE | Message is in response to a received message. This includes promotional and non-promotional messages sent inside the 24-hour standard messaging window or under the 24+1 policy. For example, use this tag to respond if a person asks for a reservation confirmation or an status update.
  +| UPDATE | Message is being sent proactively and is not in response to a received message. This includes promotional and non-promotional messages sent inside the the 24-hour standard messaging window or under the 24+1 policy.
  +| MESSAGE_TAG | Message is non-promotional and is being sent outside the 24-hour standard messaging window with a message tag. The message must match the allowed use case for the tag.
  +| NON_PROMOTIONAL_SUBSCRIPTION | Message is non-promotional, and is being sent under the subscription messaging policy by a bot with the pages_messaging_subscriptions permission.
  +
  +By default Botkit will send a `RESPONSE` messaging type when you send a simple message with `bot.reply(message, "this is a simple message"")`, `conversation.say("this is a simple message")` or `conversation.ask("this is a simple message", ...)`.
  +
  ## Use BotKit for Facebook Messenger with an Express web server
  Instead of the web server generated with setupWebserver(), it is possible to use a different web server to receive webhooks, as well as serving web pages.
  