Notify component for Facebook Messenger (#1683)

* Create notify.facebook.markdown

* Update notify.facebook.markdown

* Update notify.facebook.markdown

* Added Facebook logo

source/_components/notify.facebook.markdown

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+---
+layout: page
+title: "Facebook Messenger"
+description: "Instructions how to add user notifications to Home Assistant."
+date: 2016-12-31 14:14
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: facebook.png
+ha_category: Notifications
+ha_release: "0.35"
+---
+
+The `facebook` notification platform enables sending notifications via Facebook Messenger, powered by [Facebook](https://facebook.com).
+
+To use this notification platform in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+notify:
+  - name: NOTIFIER_NAME
+    platform: facebook
+    page_access_token: FACEBOOK_PAGE_ACCESS_TOKEN
+```
+
+Configuration variables:
+
+- **page_access_token** (*Required*): Access token for your facebook page. Checkout [Facebook Messenger Platform](https://developers.facebook.com/docs/messenger-platform/guides/setup) for more information.
+- **name** (*Optional*): Setting the optional parameter `name` allows multiple notifiers to be created. The default value is `notify`. The notifier will bind to the service `notify.NOTIFIER_NAME`.
+
+### Usage
+
+With Facebook notify service, you can send your notifications to your facebook messenger with help of your facebook page. You have to create a [Facebook Page and App](https://developers.facebook.com/docs/messenger-platform/guides/quick-start) for this service. You can control it by calling the notify service [as described here](/components/notify/). It will send a message on messenger to user specified by **target** on behalf of your page. See the [quick start](https://developers.facebook.com/docs/messenger-platform/guides/quick-start) guide for more information.
+The phone number used in **target** should be registered with facebook messenger. Phone number of the recipient should be in  +1(212)555-2368 format. If your app is not approved by facebook then the recipient should by either admin, developer or tester for your facebook app. [More...](https://developers.facebook.com/docs/messenger-platform/send-api-reference#phone_number)
+
+```yaml
+# Example automation notification entry
+automation:
+  - alias: Evening Greeting
+    trigger:
+      platform: sun
+      event: sunset
+    action:
+      service: notify.facebook
+      data:
+        message: 'Good Evening'
+        target:
+          - +919413017584
+          - +919784516314
+```