Create sensor.zestimate.markdown (#4812)

* Create sensor.zestimate.markdown

Add documentation for the Zestimate sensor.

* Incorporate MartinHjelmare changes

* Remove unnecessary configuration header

* Removed code block around the configuration tags

* Minor changes

source/_components/sensor.zestimate.markdown

@@ -0,0 +1,55 @@
+---
+layout: page
+title: "Zestimate"
+description: "Instructions on how to integrate the Zestimate sensor into Home Assistant."
+date: 2018-03-02 3:10
+sidebar: true
+comments: false
+sharing: true
+footer: true
+ha_category: Sensor
+ha_release: 0.65
+ha_iot_class: "Cloud Polling"
+---
+
+The `zestimate` sensor allows one to track the Zestimate value of properties using the [Zillow API](https://www.zillow.com/howto/api/APIOverview.htm).
+
+You will need to sign up for the Zillow API at the following link [Zillow API](https://www.zillow.com/howto/api/APIOverview.htm). You will also need the Zillow property ID for each property you'd like to track. This information is available from the URL of a property you are interested in. 
+
+For example, the White House zpid is 84074482 and can be found in it's Zillow URL: https://www.zillow.com/homedetails/1600-Pennsylvania-Ave-NW-Washington-DC-20006/84074482_zpid/
+
+To enable this sensor, add the following lines to your `configuration.yaml`.
+
+```yaml
+sensor:
+  - platform: zestimate
+    api_key: API_KEY
+    zpid:
+      - <your zpid 1>
+      - <your zpid 2>
+```
+
+{% configuration %}
+api_key:
+  description: The API key to access the service.
+  required: true
+  type: string
+zpid:
+  description: Property IDs to track in the front end.
+  required: true
+  type: list
+{% endconfiguration %}
+
+### Additional Attributes
+
+The following additional attributes are also available via the sensor.
+
+These attributes are available:
+
+- Last update
+- 30 Day change in value
+- Valuation Range High
+- Valuation Range Low
+- Address
+- Currency
+- Amount