Add DuckDNS component (#3429)

* Add DuckDNS component

* Add period and an additional line break

source/_addons/duckdns.markdown

@@ -1,6 +1,6 @@
 ---
 layout: page
-title: "Duck DNS"
+title: "DuckDNS"
 description: "Automatically update your Duck DNS IP address."
 date: 2017-04-30 13:28
 sidebar: true
@@ -10,7 +10,7 @@ footer: true
 featured: true
 ---
 
-[Duck DNS](https://duckdns.org/) is a free service which will point a DNS (sub domains of duckdns.org) to an IP of your choice.
+[Duck DNS](https://duckdns.org/) is a free dynamic DNS service. Using this service you can have a custom domainname under duckdns.org point at your home computer.
 
 ```json
 {

source/_components/duckdns.markdown

@@ -0,0 +1,36 @@
+---
+layout: page
+title: "DuckDNS"
+description: "Keep your computer registered with the DuckDNS dynamic DNS."
+date: 2017-09-23 07:08
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: duckdns.png
+ha_category: Utility
+featured: false
+ha_release: 0.55
+---
+
+With the DuckDNS component you can keep your DuckDNS record up to date. DuckDNS is a free dynamic DNS service that allows you to point a subdomain under `duckdns.org` at your computer.
+
+To use the component in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+duckdns:
+  domain: mysubdomain
+  access_token: abcdefgh
+```
+
+{% configuration binary_sensor.template %}
+  domain:
+    description: Your duckdns subdomain (without the `.duckdns.org` suffix).
+    required: true
+    type: string
+  access_token:
+    description: Your DuckDNS access token. Log in to the site to get one.
+    required: true
+    type: string
+{% endconfiguration %}