Whois Sensor (#3744)

* Init whois sensor docs

* Fixed glaring typo (hostname => domain)

source/_components/sensor.whois.markdown

@@ -0,0 +1,30 @@
+---
+layout: page
+title: "Whois Sensor"
+description: "Instructions on how to integrate WHOIS lookup sensor within Home Assistant."
+date: 2017-10-22 00:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: home-assistant.png
+ha_category: Sensor
+ha_release: "0.57"
+ha_iot_class: "Cloud Polling"
+---
+
+
+`whois` sensor allows you to perform daily WHOIS lookups against your owned domains. This provides you with information such as `expiration_date`, `name_servers`, and `registrar` details.
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  - platform: whois
+    domain: example.net
+    name: primary
+```
+
+Configuration variables:
+
+- **domain** (*Required*): The domain you want to perform WHOIS lookups against.
+- **name** (*Optional*): A friendly name to apply to this sensor.