Add mastodon docs (#5010)

source/_components/notify.mastodon.markdown

@@ -0,0 +1,52 @@
+---
+layout: page
+title: "Mastodon"
+description: "Instructions on how to add Instapush notifications to Home Assistant."
+date: 2018-03-25 18:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: mastodon.png
+ha_category: Notifications
+ha_release: 0.67
+---
+
+
+The `mastodon` platform uses [MAstodon](https://joinmastodon.org/) to delivery notifications from Home Assistant.
+
+Go to **Preferences** in the Mastodon web interface, then to **Development** and create a new application.
+
+To add Mastodon to your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+notify:
+  - name: NOTIFIER_NAME
+    platform: mastodon
+    access_token: !secret mastodon_access_token
+    client_id: !secret mastodon_client_id
+    client_secret: !secret mastodon_client_secret
+```
+
+{% configuration %}
+access_token:
+  description: Your Mastodon access token.
+  required: true
+  type: string
+client_id:
+  description: Your Mastodon client ID
+  required: true
+  type: string
+client_secret:
+  description: Your Mastodon client secret.
+  required: true
+  type: string
+base_url:
+  description: URL of the Mastodon instance to use.
+  required: false
+  type: string
+  default: https://mastodon.social
+{% endconfiguration %}
+
+To use notifications, please see the [getting started with automation page](/getting-started/automation/).