Add documentation for Kankun wifi switch. (#1665)

* Add documentation for Kankun wifi switch.

* Add documentation for missing configuration options.

source/_components/switch.kankun.markdown

@@ -0,0 +1,43 @@
+---
+layout: page
+title: "Kankun SP3 Wifi Switch"
+description: "Instructions for the Kankun SP3 wifi switch"
+date: 2016-12-28 01:50
+sidebar: true
+comments: false
+sharing: true
+footer: true
+ha_category: Switch
+ha_release: 0.36
+ha_iot_class: "Local Polling"
+---
+
+
+The `kankun` switch platform allows you to toggle customised Kankun SP3 wifi switches. Switches are
+modified to include the [json.cgi](https://github.com/homedash/kankun-json/blob/master/cgi-bin/json.cgi)
+script to provide a HTTP API. Details of the necessary modifications can be found
+[here](http://www.homeautomationforgeeks.com/openhab_http.shtml#kankun) (be sure to install the JSON version
+of the script as linked above).
+
+To enable it, add the following lines to your `configuration.yaml`:
+
+```yaml
+# Example configuration.yaml entry
+switch:
+  platform: kankun
+    switches:
+      bedroom_heating:
+        host: hostname_or_ipaddr
+```
+
+Configuration variables:
+
+- **switches** (*Required*): The array that contains all Kankun switches.
+  - **identifier** (*Required*): Name of the Kankun switch as slug. Multiple entries are possible.
+    - **host** (*Required*): Hostname or IP address of the switch on the local network.
+    - **name** (*Optional*): Friendly name of the switch.
+    - **port** (*Optional*): HTTP connection port, defaults to 80.
+    - **path** (*Optional*): Path of CGI script, defaults to `/cgi-bin/json.cgi`.
+    - **username** (*Optional*): Username for basic authentication.
+    - **password** (*Optional*): Password for basic authentication.
+